[dpdk-dev] [PATCH] kni: allow configuring the kni thread granularity

[dpdk-dev] [PATCH] kni: allow configuring the kni thread granularity

[Tudor Cornea]

The Kni kthreads seem to be re-scheduled at a granularity of roughly
1 milisecond right now, which seems to be insufficient for performing tests
involving a lot of control plane traffic.

Even if KNI_KTHREAD_RESCHEDULE_INTERVAL is set to 5 microseconds, it
seems that the existing code cannot reschedule at the desired granularily,
due to precision constraints of schedule_timeout_interruptible().

In our use case, we leverage the Linux Kernel for control plane, and
it is not uncommon to have 60K - 100K pps for some signaling protocols.

Since we are in non-atomic context, the usleep_range() function seems to be
more appropriate for being able to introduce smaller controlled delays,
in the range of 5-10 microseconds. Upon reading the existing code, it would
seem that this was the original intent. Adding sub-milisecond delays,
seems unfeasible with a call to schedule_timeout_interruptible().

KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
schedule_timeout_interruptible(
        usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));

Below, we attempted a brief comparison between the existing implementation,
which uses schedule_timeout_interruptible() and usleep_range().

insmod rte_kni.ko kthread_mode=single carrier=on

schedule_timeout_interruptible(usecs_to_jiffies(5))
kni_single CPU Usage: 2-4 %
[root@localhost ~]# ping 1.1.1.2 -I eth1
PING 1.1.1.2 (1.1.1.2) from 1.1.1.1 eth1: 56(84) bytes of data.
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.70 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.00 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.99 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.985 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.00 ms

usleep_range(5, 10)
kni_single CPU usage: 50%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.338 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.150 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.123 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.139 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.159 ms

usleep_range(20, 50)
kni_single CPU usage: 24%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.202 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.170 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.171 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.248 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.185 ms

usleep_range(50, 100)
kni_single CPU usage: 13%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.537 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.257 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.231 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.143 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.200 ms

usleep_range(100, 200)
kni_single CPU usage: 7%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.716 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.167 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.459 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.455 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.252 ms

usleep_range(1000, 1100)
kni_single CPU usage: 2%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.22 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.15 ms

Upon testing, usleep_range(1000, 1100) seems roughly equivalent in
latency and cpu usage to the variant with schedule_timeout_interruptible(),
while usleep_range(100, 200) seems to give a decent tradeoff between
latency and cpu usage, while allowing users to tweak the limits for
improved precision if they have such use cases.

Disabling RTE_KNI_PREEMPT_DEFAULT, interestingly seems to lead to a
softlockup on my kernel.

Kernel panic - not syncing: softlockup: hung tasks
CPU: 0 PID: 1226 Comm: kni_single Tainted: G        W  O 3.10 #1
 <IRQ>  [<ffffffff814f84de>] dump_stack+0x19/0x1b
 [<ffffffff814f7891>] panic+0xcd/0x1e0
 [<ffffffff810993b0>] watchdog_timer_fn+0x160/0x160
 [<ffffffff810644b2>] __run_hrtimer.isra.4+0x42/0xd0
 [<ffffffff81064b57>] hrtimer_interrupt+0xe7/0x1f0
 [<ffffffff8102cd57>] smp_apic_timer_interrupt+0x67/0xa0
 [<ffffffff8150321d>] apic_timer_interrupt+0x6d/0x80

References:
[1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt

Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>
---
 doc/guides/prog_guide/kernel_nic_interface.rst | 33 +++++++++++++++++++++++
 kernel/linux/kni/kni_dev.h                     |  2 +-
 kernel/linux/kni/kni_misc.c                    | 36 +++++++++++++++++++++++---
 3 files changed, 66 insertions(+), 5 deletions(-)

diff --git a/doc/guides/prog_guide/kernel_nic_interface.rst b/doc/guides/prog_guide/kernel_nic_interface.rst
index 1ce03ec..5d6d535 100644
--- a/doc/guides/prog_guide/kernel_nic_interface.rst
+++ b/doc/guides/prog_guide/kernel_nic_interface.rst
@@ -56,6 +56,10 @@ can be specified when the module is loaded to control its behavior:
                     off   Interfaces will be created with carrier state set to off.
                     on    Interfaces will be created with carrier state set to on.
                      (charp)
+    parm:           min_scheduling_interval: "Kni thread min scheduling interval (default=100 microseconds):
+                     (long)
+    parm:           max_scheduling_interval: "Kni thread max scheduling interval (default=200 microseconds):
+                     (long)
 
 Loading the ``rte_kni`` kernel module without any optional parameters is
 the typical way a DPDK application gets packets into and out of the kernel
@@ -174,6 +178,35 @@ To set the default carrier state to *off*:
 If the ``carrier`` parameter is not specified, the default carrier state
 of KNI interfaces will be set to *off*.
 
+KNI Kthread Scheduling
+~~~~~~~~~~~~~~~~~~~~~~
+
+The ``min_scheduling_interval`` and ``max_scheduling_interval`` parameters
+control the rescheduling interval of the KNI kthreads.
+
+This might be useful if we have use cases in which we require improved
+latency or performance for control plane traffic.
+
+The implementation is backed by Linux hrtimers, and uses ``usleep_range``.
+Hence, it will have the same granularity constraints as Linux hrtimers.
+
+To see more about the Linux hrimers, you can check the following resource: `Kernel Timers <http://www.kernel.org/doc/Documentation/timers/timers-howto.txt>`_
+
+To set the ``min_scheduling_interval`` to a value of 100 microsecnds:
+
+.. code-block:: console
+
+    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko min_scheduling_interval=100
+
+To set the ``max_scheduling_interval`` to a value of 200 microseconds:
+
+.. code-block:: console
+
+    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko max_scheduling_interval=200
+
+If the ``min_scheduling_interval`` and ``max_scheduling_interval`` parameters are
+not specified, the default interval limits will be set to *100* and *200* respectively.
+
 KNI Creation and Deletion
 -------------------------
 
diff --git a/kernel/linux/kni/kni_dev.h b/kernel/linux/kni/kni_dev.h
index c15da311..bb4d891 100644
--- a/kernel/linux/kni/kni_dev.h
+++ b/kernel/linux/kni/kni_dev.h
@@ -27,7 +27,7 @@
 #include <linux/list.h>
 
 #include <rte_kni_common.h>
-#define KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
+#define KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL 1000000 /* us */
 
 #define MBUF_BURST_SZ 32
 
diff --git a/kernel/linux/kni/kni_misc.c b/kernel/linux/kni/kni_misc.c
index 2b464c4..e23cfd9 100644
--- a/kernel/linux/kni/kni_misc.c
+++ b/kernel/linux/kni/kni_misc.c
@@ -41,6 +41,12 @@ static uint32_t multiple_kthread_on;
 static char *carrier;
 uint32_t kni_dflt_carrier;
 
+#ifdef RTE_KNI_PREEMPT_DEFAULT
+/* Kni thread scheduling interval */
+static long min_scheduling_interval = 100; /* us */
+static long max_scheduling_interval = 200; /* us */
+#endif
+
 #define KNI_DEV_IN_USE_BIT_NUM 0 /* Bit number for device in use */
 
 static int kni_net_id;
@@ -130,8 +136,7 @@ kni_thread_single(void *data)
 		up_read(&knet->kni_list_lock);
 #ifdef RTE_KNI_PREEMPT_DEFAULT
 		/* reschedule out for a while */
-		schedule_timeout_interruptible(
-			usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
+		usleep_range(min_scheduling_interval, max_scheduling_interval);
 #endif
 	}
 
@@ -150,8 +155,7 @@ kni_thread_multiple(void *param)
 			kni_net_poll_resp(dev);
 		}
 #ifdef RTE_KNI_PREEMPT_DEFAULT
-		schedule_timeout_interruptible(
-			usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
+		usleep_range(min_scheduling_interval, max_scheduling_interval);
 #endif
 	}
 
@@ -593,6 +597,16 @@ kni_init(void)
 	else
 		pr_debug("Default carrier state set to on.\n");
 
+#ifdef RTE_KNI_PREEMPT_DEFAULT
+	if (min_scheduling_interval < 0 || max_scheduling_interval < 0 ||
+		min_scheduling_interval > KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
+		max_scheduling_interval > KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
+		min_scheduling_interval >= max_scheduling_interval) {
+		pr_err("Invalid parameters for scheduling interval\n");
+		return -EINVAL;
+	}
+#endif
+
 #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
 	rc = register_pernet_subsys(&kni_net_ops);
 #else
@@ -659,3 +673,17 @@ MODULE_PARM_DESC(carrier,
 "\t\ton    Interfaces will be created with carrier state set to on.\n"
 "\t\t"
 );
+
+#ifdef RTE_KNI_PREEMPT_DEFAULT
+module_param(min_scheduling_interval, long, 0644);
+MODULE_PARM_DESC(min_scheduling_interval,
+"Kni thread min scheduling interval (default=100 microseconds):\n"
+"\t\t"
+);
+
+module_param(max_scheduling_interval, long, 0644);
+MODULE_PARM_DESC(max_scheduling_interval,
+"Kni thread max scheduling interval (default=200 microseconds):\n"
+"\t\t"
+);
+#endif
-- 
2.7.4

[dpdk-dev] [PATCH v2] kni: allow configuring the kni thread granularity

[Tudor Cornea]

The Kni kthreads seem to be re-scheduled at a granularity of roughly
1 millisecond right now, which seems to be insufficient for performing tests
involving a lot of control plane traffic.

Even if KNI_KTHREAD_RESCHEDULE_INTERVAL is set to 5 microseconds, it
seems that the existing code cannot reschedule at the desired granularily,
due to precision constraints of schedule_timeout_interruptible().

In our use case, we leverage the Linux Kernel for control plane, and
it is not uncommon to have 60K - 100K pps for some signaling protocols.

Since we are in non-atomic context, the usleep_range() function seems to be
more appropriate for being able to introduce smaller controlled delays,
in the range of 5-10 microseconds. Upon reading the existing code, it would
seem that this was the original intent. Adding sub-millisecond delays,
seems unfeasible with a call to schedule_timeout_interruptible().

KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
schedule_timeout_interruptible(
        usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));

Below, we attempted a brief comparison between the existing implementation,
which uses schedule_timeout_interruptible() and usleep_range().

insmod rte_kni.ko kthread_mode=single carrier=on

schedule_timeout_interruptible(usecs_to_jiffies(5))
kni_single CPU Usage: 2-4 %
[root@localhost ~]# ping 1.1.1.2 -I eth1
PING 1.1.1.2 (1.1.1.2) from 1.1.1.1 eth1: 56(84) bytes of data.
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.70 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.00 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.99 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.985 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.00 ms

usleep_range(5, 10)
kni_single CPU usage: 50%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.338 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.150 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.123 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.139 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.159 ms

usleep_range(20, 50)
kni_single CPU usage: 24%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.202 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.170 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.171 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.248 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.185 ms

usleep_range(50, 100)
kni_single CPU usage: 13%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.537 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.257 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.231 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.143 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.200 ms

usleep_range(100, 200)
kni_single CPU usage: 7%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.716 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.167 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.459 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.455 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.252 ms

usleep_range(1000, 1100)
kni_single CPU usage: 2%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.22 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.15 ms

Upon testing, usleep_range(1000, 1100) seems roughly equivalent in
latency and cpu usage to the variant with schedule_timeout_interruptible(),
while usleep_range(100, 200) seems to give a decent tradeoff between
latency and cpu usage, while allowing users to tweak the limits for
improved precision if they have such use cases.

Disabling RTE_KNI_PREEMPT_DEFAULT, interestingly seems to lead to a
softlockup on my kernel.

Kernel panic - not syncing: softlockup: hung tasks
CPU: 0 PID: 1226 Comm: kni_single Tainted: G        W  O 3.10 #1
 <IRQ>  [<ffffffff814f84de>] dump_stack+0x19/0x1b
 [<ffffffff814f7891>] panic+0xcd/0x1e0
 [<ffffffff810993b0>] watchdog_timer_fn+0x160/0x160
 [<ffffffff810644b2>] __run_hrtimer.isra.4+0x42/0xd0
 [<ffffffff81064b57>] hrtimer_interrupt+0xe7/0x1f0
 [<ffffffff8102cd57>] smp_apic_timer_interrupt+0x67/0xa0
 [<ffffffff8150321d>] apic_timer_interrupt+0x6d/0x80

References:
[1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt

Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>

---
v2:
* Fixed some spelling errors
---
 doc/guides/prog_guide/kernel_nic_interface.rst | 33 +++++++++++++++++++++++
 kernel/linux/kni/kni_dev.h                     |  2 +-
 kernel/linux/kni/kni_misc.c                    | 36 +++++++++++++++++++++++---
 3 files changed, 66 insertions(+), 5 deletions(-)

diff --git a/doc/guides/prog_guide/kernel_nic_interface.rst b/doc/guides/prog_guide/kernel_nic_interface.rst
index 1ce03ec..2dd3481 100644
--- a/doc/guides/prog_guide/kernel_nic_interface.rst
+++ b/doc/guides/prog_guide/kernel_nic_interface.rst
@@ -56,6 +56,10 @@ can be specified when the module is loaded to control its behavior:
                     off   Interfaces will be created with carrier state set to off.
                     on    Interfaces will be created with carrier state set to on.
                      (charp)
+    parm:           min_scheduling_interval: "Kni thread min scheduling interval (default=100 microseconds):
+                     (long)
+    parm:           max_scheduling_interval: "Kni thread max scheduling interval (default=200 microseconds):
+                     (long)
 
 Loading the ``rte_kni`` kernel module without any optional parameters is
 the typical way a DPDK application gets packets into and out of the kernel
@@ -174,6 +178,35 @@ To set the default carrier state to *off*:
 If the ``carrier`` parameter is not specified, the default carrier state
 of KNI interfaces will be set to *off*.
 
+KNI Kthread Scheduling
+~~~~~~~~~~~~~~~~~~~~~~
+
+The ``min_scheduling_interval`` and ``max_scheduling_interval`` parameters
+control the rescheduling interval of the KNI kthreads.
+
+This might be useful if we have use cases in which we require improved
+latency or performance for control plane traffic.
+
+The implementation is backed by Linux hrtimers, and uses ``usleep_range``.
+Hence, it will have the same granularity constraints as Linux hrtimers.
+
+To see more about the Linux hrtimers, you can check the following resource: `Kernel Timers <http://www.kernel.org/doc/Documentation/timers/timers-howto.txt>`_
+
+To set the ``min_scheduling_interval`` to a value of 100 microseconds:
+
+.. code-block:: console
+
+    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko min_scheduling_interval=100
+
+To set the ``max_scheduling_interval`` to a value of 200 microseconds:
+
+.. code-block:: console
+
+    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko max_scheduling_interval=200
+
+If the ``min_scheduling_interval`` and ``max_scheduling_interval`` parameters are
+not specified, the default interval limits will be set to *100* and *200* respectively.
+
 KNI Creation and Deletion
 -------------------------
 
diff --git a/kernel/linux/kni/kni_dev.h b/kernel/linux/kni/kni_dev.h
index c15da311..bb4d891 100644
--- a/kernel/linux/kni/kni_dev.h
+++ b/kernel/linux/kni/kni_dev.h
@@ -27,7 +27,7 @@
 #include <linux/list.h>
 
 #include <rte_kni_common.h>
-#define KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
+#define KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL 1000000 /* us */
 
 #define MBUF_BURST_SZ 32
 
diff --git a/kernel/linux/kni/kni_misc.c b/kernel/linux/kni/kni_misc.c
index 2b464c4..e23cfd9 100644
--- a/kernel/linux/kni/kni_misc.c
+++ b/kernel/linux/kni/kni_misc.c
@@ -41,6 +41,12 @@ static uint32_t multiple_kthread_on;
 static char *carrier;
 uint32_t kni_dflt_carrier;
 
+#ifdef RTE_KNI_PREEMPT_DEFAULT
+/* Kni thread scheduling interval */
+static long min_scheduling_interval = 100; /* us */
+static long max_scheduling_interval = 200; /* us */
+#endif
+
 #define KNI_DEV_IN_USE_BIT_NUM 0 /* Bit number for device in use */
 
 static int kni_net_id;
@@ -130,8 +136,7 @@ kni_thread_single(void *data)
 		up_read(&knet->kni_list_lock);
 #ifdef RTE_KNI_PREEMPT_DEFAULT
 		/* reschedule out for a while */
-		schedule_timeout_interruptible(
-			usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
+		usleep_range(min_scheduling_interval, max_scheduling_interval);
 #endif
 	}
 
@@ -150,8 +155,7 @@ kni_thread_multiple(void *param)
 			kni_net_poll_resp(dev);
 		}
 #ifdef RTE_KNI_PREEMPT_DEFAULT
-		schedule_timeout_interruptible(
-			usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
+		usleep_range(min_scheduling_interval, max_scheduling_interval);
 #endif
 	}
 
@@ -593,6 +597,16 @@ kni_init(void)
 	else
 		pr_debug("Default carrier state set to on.\n");
 
+#ifdef RTE_KNI_PREEMPT_DEFAULT
+	if (min_scheduling_interval < 0 || max_scheduling_interval < 0 ||
+		min_scheduling_interval > KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
+		max_scheduling_interval > KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
+		min_scheduling_interval >= max_scheduling_interval) {
+		pr_err("Invalid parameters for scheduling interval\n");
+		return -EINVAL;
+	}
+#endif
+
 #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
 	rc = register_pernet_subsys(&kni_net_ops);
 #else
@@ -659,3 +673,17 @@ MODULE_PARM_DESC(carrier,
 "\t\ton    Interfaces will be created with carrier state set to on.\n"
 "\t\t"
 );
+
+#ifdef RTE_KNI_PREEMPT_DEFAULT
+module_param(min_scheduling_interval, long, 0644);
+MODULE_PARM_DESC(min_scheduling_interval,
+"Kni thread min scheduling interval (default=100 microseconds):\n"
+"\t\t"
+);
+
+module_param(max_scheduling_interval, long, 0644);
+MODULE_PARM_DESC(max_scheduling_interval,
+"Kni thread max scheduling interval (default=200 microseconds):\n"
+"\t\t"
+);
+#endif
-- 
2.7.4

Re: [dpdk-dev] [PATCH v2] kni: allow configuring the kni thread granularity

[Stephen Hemminger]

On Tue,  2 Nov 2021 17:51:13 +0200
Tudor Cornea <tudor.cornea@gmail.com> wrote:

> +#ifdef RTE_KNI_PREEMPT_DEFAULT
> +module_param(min_scheduling_interval, long, 0644);
> +MODULE_PARM_DESC(min_scheduling_interval,
> +"Kni thread min scheduling interval (default=100 microseconds):\n"
> +"\t\t"
> +);

Why the non-standard newline's and tab's?
Please try to make KNI look like other kernel code.

Re: [dpdk-dev] [PATCH v2] kni: allow configuring the kni thread granularity

[Tudor Cornea]

On Tue, 2 Nov 2021 at 17:53, Stephen Hemminger <stephen@networkplumber.org>
wrote:

> On Tue,  2 Nov 2021 17:51:13 +0200
> Tudor Cornea <tudor.cornea@gmail.com> wrote:
>
> > +#ifdef RTE_KNI_PREEMPT_DEFAULT
> > +module_param(min_scheduling_interval, long, 0644);
> > +MODULE_PARM_DESC(min_scheduling_interval,
> > +"Kni thread min scheduling interval (default=100 microseconds):\n"
> > +"\t\t"
> > +);
>
> Why the non-standard newline's and tab's?
> Please try to make KNI look like other kernel code.
>

Hi Stephen,

I tried to base the description of the new parameters on an existing
parameter implemented for the rte_kni module - carrier.

module_param(carrier, charp, 0644);
MODULE_PARM_DESC(carrier,
"Default carrier state for KNI interface (default=off):\n"
"\t\toff   Interfaces will be created with carrier state set to off.\n"
"\t\ton    Interfaces will be created with carrier state set to on.\n"
"\t\t"
);

I thought about keeping the compatibility in terms of coding style with the
existing Kni module parameters.
Upon browsing the Linux tree, I realise it might not be standard (
checkpatch.pl , interestingly didn't seem to complain about the patch)

I also realise now, that I missed two tabs at the beginning of the params
description.
Should I add the missing tabs, so that the new parameters that I intend to
add through this patch are similar in style to the existing ones, or should
I remove the newlines and tabs altogether, when specifying the description
for min_scheduling_interval and max_scheduling_interval ?

Thanks,
Tudor

Re: [dpdk-dev] [PATCH v2] kni: allow configuring the kni thread granularity

[Stephen Hemminger]

On Wed, 3 Nov 2021 22:40:51 +0200
Tudor Cornea <tudor.cornea@gmail.com> wrote:

> On Tue, 2 Nov 2021 at 17:53, Stephen Hemminger <stephen@networkplumber.org>
> wrote:
> 
> > On Tue,  2 Nov 2021 17:51:13 +0200
> > Tudor Cornea <tudor.cornea@gmail.com> wrote:
> >  
> > > +#ifdef RTE_KNI_PREEMPT_DEFAULT
> > > +module_param(min_scheduling_interval, long, 0644);
> > > +MODULE_PARM_DESC(min_scheduling_interval,
> > > +"Kni thread min scheduling interval (default=100 microseconds):\n"
> > > +"\t\t"
> > > +);  
> >
> > Why the non-standard newline's and tab's?
> > Please try to make KNI look like other kernel code.
> >  
> 
> Hi Stephen,
> 
> I tried to base the description of the new parameters on an existing
> parameter implemented for the rte_kni module - carrier.
> 
> module_param(carrier, charp, 0644);
> MODULE_PARM_DESC(carrier,
> "Default carrier state for KNI interface (default=off):\n"
> "\t\toff   Interfaces will be created with carrier state set to off.\n"
> "\t\ton    Interfaces will be created with carrier state set to on.\n"
> "\t\t"
> );
> 
> I thought about keeping the compatibility in terms of coding style with the
> existing Kni module parameters.
> Upon browsing the Linux tree, I realise it might not be standard (
> checkpatch.pl , interestingly didn't seem to complain about the patch)
> 
> I also realise now, that I missed two tabs at the beginning of the params
> description.
> Should I add the missing tabs, so that the new parameters that I intend to
> add through this patch are similar in style to the existing ones, or should
> I remove the newlines and tabs altogether, when specifying the description
> for min_scheduling_interval and max_scheduling_interval ?
> 
> Thanks,
> Tudor

Although KNI is unlikely to ever get upstream code review, there
is no reason to deviate from common practice in kernel drivers.
The original module parameter was doing something unconventional.

Not wrong, just different.

[dpdk-dev] [PATCH v3] kni: allow configuring the kni thread granularity

[Tudor Cornea]

The Kni kthreads seem to be re-scheduled at a granularity of roughly
1 millisecond right now, which seems to be insufficient for performing
tests involving a lot of control plane traffic.

Even if KNI_KTHREAD_RESCHEDULE_INTERVAL is set to 5 microseconds, it
seems that the existing code cannot reschedule at the desired granularily,
due to precision constraints of schedule_timeout_interruptible().

In our use case, we leverage the Linux Kernel for control plane, and
it is not uncommon to have 60K - 100K pps for some signaling protocols.

Since we are not in atomic context, the usleep_range() function seems to be
more appropriate for being able to introduce smaller controlled delays,
in the range of 5-10 microseconds. Upon reading the existing code, it would
seem that this was the original intent. Adding sub-millisecond delays,
seems unfeasible with a call to schedule_timeout_interruptible().

KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
schedule_timeout_interruptible(
        usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));

Below, we attempted a brief comparison between the existing implementation,
which uses schedule_timeout_interruptible() and usleep_range().

We attempt to measure the CPU usage, and RTT between two Kni interfaces,
which are created on top of vmxnet3 adapters, connected by a vSwitch.

insmod rte_kni.ko kthread_mode=single carrier=on

schedule_timeout_interruptible(usecs_to_jiffies(5))
kni_single CPU Usage: 2-4 %
[root@localhost ~]# ping 1.1.1.2 -I eth1
PING 1.1.1.2 (1.1.1.2) from 1.1.1.1 eth1: 56(84) bytes of data.
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.70 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.00 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.99 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.985 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.00 ms

usleep_range(5, 10)
kni_single CPU usage: 50%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.338 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.150 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.123 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.139 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.159 ms

usleep_range(20, 50)
kni_single CPU usage: 24%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.202 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.170 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.171 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.248 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.185 ms

usleep_range(50, 100)
kni_single CPU usage: 13%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.537 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.257 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.231 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.143 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.200 ms

usleep_range(100, 200)
kni_single CPU usage: 7%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.716 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.167 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.459 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.455 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.252 ms

usleep_range(1000, 1100)
kni_single CPU usage: 2%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.22 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.15 ms

Upon testing, usleep_range(1000, 1100) seems roughly equivalent in
latency and cpu usage to the variant with schedule_timeout_interruptible(),
while usleep_range(100, 200) seems to give a decent tradeoff between
latency and cpu usage, while allowing users to tweak the limits for
improved precision if they have such use cases.

Disabling RTE_KNI_PREEMPT_DEFAULT, interestingly seems to lead to a
softlockup on my kernel.

Kernel panic - not syncing: softlockup: hung tasks
CPU: 0 PID: 1226 Comm: kni_single Tainted: G        W  O 3.10 #1
 <IRQ>  [<ffffffff814f84de>] dump_stack+0x19/0x1b
 [<ffffffff814f7891>] panic+0xcd/0x1e0
 [<ffffffff810993b0>] watchdog_timer_fn+0x160/0x160
 [<ffffffff810644b2>] __run_hrtimer.isra.4+0x42/0xd0
 [<ffffffff81064b57>] hrtimer_interrupt+0xe7/0x1f0
 [<ffffffff8102cd57>] smp_apic_timer_interrupt+0x67/0xa0
 [<ffffffff8150321d>] apic_timer_interrupt+0x6d/0x80

References:
[1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt

Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>

---
v3:
* Fixed unwrapped commit description warning
* Changed from hrtimers to Linux High Precision Timers in docs
* Added two tabs at the beginning of the new params description.
  Stephen correctly pointed out that the descriptions of the parameters
  for the Kni module are nonstandard w.r.t existing kernel code.
  I was thinking to preserve compatibility with the existing parameters
  of the Kni module for the moment, while an additional clean-up patch
  could format the descriptions to be closer to the kernel standard.
v2:
* Fixed some spelling errors
---
 doc/guides/prog_guide/kernel_nic_interface.rst | 33 +++++++++++++++++++++++
 kernel/linux/kni/kni_dev.h                     |  2 +-
 kernel/linux/kni/kni_misc.c                    | 36 +++++++++++++++++++++++---
 3 files changed, 66 insertions(+), 5 deletions(-)

diff --git a/doc/guides/prog_guide/kernel_nic_interface.rst b/doc/guides/prog_guide/kernel_nic_interface.rst
index 1ce03ec..fce3667 100644
--- a/doc/guides/prog_guide/kernel_nic_interface.rst
+++ b/doc/guides/prog_guide/kernel_nic_interface.rst
@@ -56,6 +56,10 @@ can be specified when the module is loaded to control its behavior:
                     off   Interfaces will be created with carrier state set to off.
                     on    Interfaces will be created with carrier state set to on.
                      (charp)
+    parm:           min_scheduling_interval: "Kni thread min scheduling interval (default=100 microseconds):
+                     (long)
+    parm:           max_scheduling_interval: "Kni thread max scheduling interval (default=200 microseconds):
+                     (long)
 
 Loading the ``rte_kni`` kernel module without any optional parameters is
 the typical way a DPDK application gets packets into and out of the kernel
@@ -174,6 +178,35 @@ To set the default carrier state to *off*:
 If the ``carrier`` parameter is not specified, the default carrier state
 of KNI interfaces will be set to *off*.
 
+KNI Kthread Scheduling
+~~~~~~~~~~~~~~~~~~~~~~
+
+The ``min_scheduling_interval`` and ``max_scheduling_interval`` parameters
+control the rescheduling interval of the KNI kthreads.
+
+This might be useful if we have use cases in which we require improved
+latency or performance for control plane traffic.
+
+The implementation is backed by Linux High Precision Timers, and uses ``usleep_range``.
+Hence, it will have the same granularity constraints as this Linux subsystem.
+
+For Linux High Precision Timers, you can check the following resource: `Kernel Timers <http://www.kernel.org/doc/Documentation/timers/timers-howto.txt>`_
+
+To set the ``min_scheduling_interval`` to a value of 100 microseconds:
+
+.. code-block:: console
+
+    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko min_scheduling_interval=100
+
+To set the ``max_scheduling_interval`` to a value of 200 microseconds:
+
+.. code-block:: console
+
+    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko max_scheduling_interval=200
+
+If the ``min_scheduling_interval`` and ``max_scheduling_interval`` parameters are
+not specified, the default interval limits will be set to *100* and *200* respectively.
+
 KNI Creation and Deletion
 -------------------------
 
diff --git a/kernel/linux/kni/kni_dev.h b/kernel/linux/kni/kni_dev.h
index c15da311..bb4d891 100644
--- a/kernel/linux/kni/kni_dev.h
+++ b/kernel/linux/kni/kni_dev.h
@@ -27,7 +27,7 @@
 #include <linux/list.h>
 
 #include <rte_kni_common.h>
-#define KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
+#define KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL 1000000 /* us */
 
 #define MBUF_BURST_SZ 32
 
diff --git a/kernel/linux/kni/kni_misc.c b/kernel/linux/kni/kni_misc.c
index 2b464c4..1bfa33f 100644
--- a/kernel/linux/kni/kni_misc.c
+++ b/kernel/linux/kni/kni_misc.c
@@ -41,6 +41,12 @@ static uint32_t multiple_kthread_on;
 static char *carrier;
 uint32_t kni_dflt_carrier;
 
+#ifdef RTE_KNI_PREEMPT_DEFAULT
+/* Kni thread scheduling interval */
+static long min_scheduling_interval = 100; /* us */
+static long max_scheduling_interval = 200; /* us */
+#endif
+
 #define KNI_DEV_IN_USE_BIT_NUM 0 /* Bit number for device in use */
 
 static int kni_net_id;
@@ -130,8 +136,7 @@ kni_thread_single(void *data)
 		up_read(&knet->kni_list_lock);
 #ifdef RTE_KNI_PREEMPT_DEFAULT
 		/* reschedule out for a while */
-		schedule_timeout_interruptible(
-			usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
+		usleep_range(min_scheduling_interval, max_scheduling_interval);
 #endif
 	}
 
@@ -150,8 +155,7 @@ kni_thread_multiple(void *param)
 			kni_net_poll_resp(dev);
 		}
 #ifdef RTE_KNI_PREEMPT_DEFAULT
-		schedule_timeout_interruptible(
-			usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
+		usleep_range(min_scheduling_interval, max_scheduling_interval);
 #endif
 	}
 
@@ -593,6 +597,16 @@ kni_init(void)
 	else
 		pr_debug("Default carrier state set to on.\n");
 
+#ifdef RTE_KNI_PREEMPT_DEFAULT
+	if (min_scheduling_interval < 0 || max_scheduling_interval < 0 ||
+		min_scheduling_interval > KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
+		max_scheduling_interval > KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
+		min_scheduling_interval >= max_scheduling_interval) {
+		pr_err("Invalid parameters for scheduling interval\n");
+		return -EINVAL;
+	}
+#endif
+
 #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
 	rc = register_pernet_subsys(&kni_net_ops);
 #else
@@ -659,3 +673,17 @@ MODULE_PARM_DESC(carrier,
 "\t\ton    Interfaces will be created with carrier state set to on.\n"
 "\t\t"
 );
+
+#ifdef RTE_KNI_PREEMPT_DEFAULT
+module_param(min_scheduling_interval, long, 0644);
+MODULE_PARM_DESC(min_scheduling_interval,
+"\t\tKni thread min scheduling interval (default=100 microseconds):\n"
+"\t\t"
+);
+
+module_param(max_scheduling_interval, long, 0644);
+MODULE_PARM_DESC(max_scheduling_interval,
+"\t\tKni thread max scheduling interval (default=200 microseconds):\n"
+"\t\t"
+);
+#endif
-- 
2.7.4

Re: [PATCH v3] kni: allow configuring the kni thread granularity

[Ferruh Yigit]

On 11/8/2021 10:13 AM, Tudor Cornea wrote:
> The Kni kthreads seem to be re-scheduled at a granularity of roughly
> 1 millisecond right now, which seems to be insufficient for performing
> tests involving a lot of control plane traffic.
> 
> Even if KNI_KTHREAD_RESCHEDULE_INTERVAL is set to 5 microseconds, it
> seems that the existing code cannot reschedule at the desired granularily,
> due to precision constraints of schedule_timeout_interruptible().
> 

ack

> In our use case, we leverage the Linux Kernel for control plane, and
> it is not uncommon to have 60K - 100K pps for some signaling protocols.
> 
> Since we are not in atomic context, the usleep_range() function seems to be
> more appropriate for being able to introduce smaller controlled delays,
> in the range of 5-10 microseconds. Upon reading the existing code, it would
> seem that this was the original intent. Adding sub-millisecond delays,
> seems unfeasible with a call to schedule_timeout_interruptible().
>> KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
> schedule_timeout_interruptible(
>          usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
> 

Agree, although comment highlights that intention is to have microsecond
current code doesn't provide it.

> Below, we attempted a brief comparison between the existing implementation,
> which uses schedule_timeout_interruptible() and usleep_range().
> 

+1 to use 'usleep_range()'.

Overall +1 to the change, I think it fixes the kernel thread delay, and
makes it configurable. As you clarified below, making the polls too frequent
cause too much CPU consumption, so it is good idea to make it configurable.

Let me test the code first, I think it is too late for this release, but
we can get it for next release if the testing goes well.

> We attempt to measure the CPU usage, and RTT between two Kni interfaces,
> which are created on top of vmxnet3 adapters, connected by a vSwitch.
> 
> insmod rte_kni.ko kthread_mode=single carrier=on
> 
> schedule_timeout_interruptible(usecs_to_jiffies(5))
> kni_single CPU Usage: 2-4 %
> [root@localhost ~]# ping 1.1.1.2 -I eth1
> PING 1.1.1.2 (1.1.1.2) from 1.1.1.1 eth1: 56(84) bytes of data.
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.70 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.00 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.99 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.985 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.00 ms
> 
> usleep_range(5, 10)
> kni_single CPU usage: 50%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.338 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.150 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.123 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.139 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.159 ms
> 
> usleep_range(20, 50)
> kni_single CPU usage: 24%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.202 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.170 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.171 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.248 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.185 ms
> 
> usleep_range(50, 100)
> kni_single CPU usage: 13%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.537 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.257 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.231 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.143 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.200 ms
> 
> usleep_range(100, 200)
> kni_single CPU usage: 7%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.716 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.167 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.459 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.455 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.252 ms
> 
> usleep_range(1000, 1100)
> kni_single CPU usage: 2%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.22 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.15 ms
> 
> Upon testing, usleep_range(1000, 1100) seems roughly equivalent in
> latency and cpu usage to the variant with schedule_timeout_interruptible(),
> while usleep_range(100, 200) seems to give a decent tradeoff between
> latency and cpu usage, while allowing users to tweak the limits for
> improved precision if they have such use cases.
> 
> Disabling RTE_KNI_PREEMPT_DEFAULT, interestingly seems to lead to a
> softlockup on my kernel.
> 

Same here. That is why I wonder if there is a point to keep the compile
time flag?
Since we can't unset it practically, and now the delay can be configurable
by module parameters, what do you think to remove the compile time flag
completely?

> Kernel panic - not syncing: softlockup: hung tasks
> CPU: 0 PID: 1226 Comm: kni_single Tainted: G        W  O 3.10 #1
>   <IRQ>  [<ffffffff814f84de>] dump_stack+0x19/0x1b
>   [<ffffffff814f7891>] panic+0xcd/0x1e0
>   [<ffffffff810993b0>] watchdog_timer_fn+0x160/0x160
>   [<ffffffff810644b2>] __run_hrtimer.isra.4+0x42/0xd0
>   [<ffffffff81064b57>] hrtimer_interrupt+0xe7/0x1f0
>   [<ffffffff8102cd57>] smp_apic_timer_interrupt+0x67/0xa0
>   [<ffffffff8150321d>] apic_timer_interrupt+0x6d/0x80
> 
> References:
> [1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt
> 
> Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>
> 

<...>

Re: [PATCH v3] kni: allow configuring the kni thread granularity

[Ferruh Yigit]

On 11/22/2021 5:31 PM, Ferruh Yigit wrote:
> On 11/8/2021 10:13 AM, Tudor Cornea wrote:
>> The Kni kthreads seem to be re-scheduled at a granularity of roughly
>> 1 millisecond right now, which seems to be insufficient for performing
>> tests involving a lot of control plane traffic.
>>
>> Even if KNI_KTHREAD_RESCHEDULE_INTERVAL is set to 5 microseconds, it
>> seems that the existing code cannot reschedule at the desired granularily,
>> due to precision constraints of schedule_timeout_interruptible().
>>
> 
> ack
> 
>> In our use case, we leverage the Linux Kernel for control plane, and
>> it is not uncommon to have 60K - 100K pps for some signaling protocols.
>>
>> Since we are not in atomic context, the usleep_range() function seems to be
>> more appropriate for being able to introduce smaller controlled delays,
>> in the range of 5-10 microseconds. Upon reading the existing code, it would
>> seem that this was the original intent. Adding sub-millisecond delays,
>> seems unfeasible with a call to schedule_timeout_interruptible().
>>> KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
>> schedule_timeout_interruptible(
>>          usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
>>
> 
> Agree, although comment highlights that intention is to have microsecond
> current code doesn't provide it.
> 
>> Below, we attempted a brief comparison between the existing implementation,
>> which uses schedule_timeout_interruptible() and usleep_range().
>>
> 
> +1 to use 'usleep_range()'.
> 
> Overall +1 to the change, I think it fixes the kernel thread delay, and
> makes it configurable. As you clarified below, making the polls too frequent
> cause too much CPU consumption, so it is good idea to make it configurable.
> 
> Let me test the code first, I think it is too late for this release, but
> we can get it for next release if the testing goes well.
> 

As I tested both with KNI sample app and KNI PMD, change looks good,
practically we can't change the scheduler delay with existing code but
this patch enables it and lets configure performance/CPU usage trade of.

Only possible change is to remove 'RTE_KNI_PREEMPT_DEFAULT' macro as
mentioned below.

>> We attempt to measure the CPU usage, and RTT between two Kni interfaces,
>> which are created on top of vmxnet3 adapters, connected by a vSwitch.
>>
>> insmod rte_kni.ko kthread_mode=single carrier=on
>>
>> schedule_timeout_interruptible(usecs_to_jiffies(5))
>> kni_single CPU Usage: 2-4 %
>> [root@localhost ~]# ping 1.1.1.2 -I eth1
>> PING 1.1.1.2 (1.1.1.2) from 1.1.1.1 eth1: 56(84) bytes of data.
>> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.70 ms
>> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.00 ms
>> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.99 ms
>> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.985 ms
>> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.00 ms
>>
>> usleep_range(5, 10)
>> kni_single CPU usage: 50%
>> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.338 ms
>> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.150 ms
>> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.123 ms
>> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.139 ms
>> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.159 ms
>>
>> usleep_range(20, 50)
>> kni_single CPU usage: 24%
>> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.202 ms
>> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.170 ms
>> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.171 ms
>> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.248 ms
>> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.185 ms
>>
>> usleep_range(50, 100)
>> kni_single CPU usage: 13%
>> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.537 ms
>> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.257 ms
>> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.231 ms
>> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.143 ms
>> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.200 ms
>>
>> usleep_range(100, 200)
>> kni_single CPU usage: 7%
>> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.716 ms
>> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.167 ms
>> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.459 ms
>> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.455 ms
>> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.252 ms
>>
>> usleep_range(1000, 1100)
>> kni_single CPU usage: 2%
>> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.22 ms
>> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.17 ms
>> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.17 ms
>> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=1.17 ms
>> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.15 ms
>>
>> Upon testing, usleep_range(1000, 1100) seems roughly equivalent in
>> latency and cpu usage to the variant with schedule_timeout_interruptible(),
>> while usleep_range(100, 200) seems to give a decent tradeoff between
>> latency and cpu usage, while allowing users to tweak the limits for
>> improved precision if they have such use cases.
>>
>> Disabling RTE_KNI_PREEMPT_DEFAULT, interestingly seems to lead to a
>> softlockup on my kernel.
>>
> 
> Same here. That is why I wonder if there is a point to keep the compile
> time flag?
> Since we can't unset it practically, and now the delay can be configurable
> by module parameters, what do you think to remove the compile time flag
> completely?
> 
>> Kernel panic - not syncing: softlockup: hung tasks
>> CPU: 0 PID: 1226 Comm: kni_single Tainted: G        W  O 3.10 #1
>>   <IRQ>  [<ffffffff814f84de>] dump_stack+0x19/0x1b
>>   [<ffffffff814f7891>] panic+0xcd/0x1e0
>>   [<ffffffff810993b0>] watchdog_timer_fn+0x160/0x160
>>   [<ffffffff810644b2>] __run_hrtimer.isra.4+0x42/0xd0
>>   [<ffffffff81064b57>] hrtimer_interrupt+0xe7/0x1f0
>>   [<ffffffff8102cd57>] smp_apic_timer_interrupt+0x67/0xa0
>>   [<ffffffff8150321d>] apic_timer_interrupt+0x6d/0x80
>>
>> References:
>> [1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt
>>
>> Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>
>>
> 
> <...>

Re: [PATCH v3] kni: allow configuring the kni thread granularity

[Tudor Cornea]

[-- Attachment #1: Type: text/plain, Size: 453 bytes --]

Hi Ferruh,



> As I tested both with KNI sample app and KNI PMD, change looks good,
> practically we can't change the scheduler delay with existing code but
> this patch enables it and lets configure performance/CPU usage trade of.
>
> Only possible change is to remove 'RTE_KNI_PREEMPT_DEFAULT' macro as
> mentioned below.
>
>
Thanks for the suggestion.
I will send an updated version of the patch, which will remove the
RTE_KNI_PREEMPT_DEFAULT macro

[-- Attachment #2: Type: text/html, Size: 770 bytes --]

[PATCH v4] kni: allow configuring the kni thread granularity

[Tudor Cornea]

The Kni kthreads seem to be re-scheduled at a granularity of roughly
1 millisecond right now, which seems to be insufficient for performing
tests involving a lot of control plane traffic.

Even if KNI_KTHREAD_RESCHEDULE_INTERVAL is set to 5 microseconds, it
seems that the existing code cannot reschedule at the desired granularily,
due to precision constraints of schedule_timeout_interruptible().

In our use case, we leverage the Linux Kernel for control plane, and
it is not uncommon to have 60K - 100K pps for some signaling protocols.

Since we are not in atomic context, the usleep_range() function seems to be
more appropriate for being able to introduce smaller controlled delays,
in the range of 5-10 microseconds. Upon reading the existing code, it would
seem that this was the original intent. Adding sub-millisecond delays,
seems unfeasible with a call to schedule_timeout_interruptible().

KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
schedule_timeout_interruptible(
        usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));

Below, we attempted a brief comparison between the existing implementation,
which uses schedule_timeout_interruptible() and usleep_range().

We attempt to measure the CPU usage, and RTT between two Kni interfaces,
which are created on top of vmxnet3 adapters, connected by a vSwitch.

insmod rte_kni.ko kthread_mode=single carrier=on

schedule_timeout_interruptible(usecs_to_jiffies(5))
kni_single CPU Usage: 2-4 %
[root@localhost ~]# ping 1.1.1.2 -I eth1
PING 1.1.1.2 (1.1.1.2) from 1.1.1.1 eth1: 56(84) bytes of data.
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.70 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.00 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.99 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.985 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.00 ms

usleep_range(5, 10)
kni_single CPU usage: 50%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.338 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.150 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.123 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.139 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.159 ms

usleep_range(20, 50)
kni_single CPU usage: 24%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.202 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.170 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.171 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.248 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.185 ms

usleep_range(50, 100)
kni_single CPU usage: 13%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.537 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.257 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.231 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.143 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.200 ms

usleep_range(100, 200)
kni_single CPU usage: 7%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.716 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.167 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.459 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.455 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.252 ms

usleep_range(1000, 1100)
kni_single CPU usage: 2%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.22 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.15 ms

Upon testing, usleep_range(1000, 1100) seems roughly equivalent in
latency and cpu usage to the variant with schedule_timeout_interruptible(),
while usleep_range(100, 200) seems to give a decent tradeoff between
latency and cpu usage, while allowing users to tweak the limits for
improved precision if they have such use cases.

Disabling RTE_KNI_PREEMPT_DEFAULT, interestingly seems to lead to a
softlockup on my kernel.

Kernel panic - not syncing: softlockup: hung tasks
CPU: 0 PID: 1226 Comm: kni_single Tainted: G        W  O 3.10 #1
 <IRQ>  [<ffffffff814f84de>] dump_stack+0x19/0x1b
 [<ffffffff814f7891>] panic+0xcd/0x1e0
 [<ffffffff810993b0>] watchdog_timer_fn+0x160/0x160
 [<ffffffff810644b2>] __run_hrtimer.isra.4+0x42/0xd0
 [<ffffffff81064b57>] hrtimer_interrupt+0xe7/0x1f0
 [<ffffffff8102cd57>] smp_apic_timer_interrupt+0x67/0xa0
 [<ffffffff8150321d>] apic_timer_interrupt+0x6d/0x80

This patch also attempts to remove this option.

References:
[1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt

Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>

---
v4:
* Removed RTE_KNI_PREEMPT_DEFAULT configuration option
v3:
* Fixed unwrapped commit description warning
* Changed from hrtimers to Linux High Precision Timers in docs
* Added two tabs at the beginning of the new params description.
  Stephen correctly pointed out that the descriptions of the parameters
  for the Kni module are nonstandard w.r.t existing kernel code.
  I was thinking to preserve compatibility with the existing parameters
  of the Kni module for the moment, while an additional clean-up patch
  could format the descriptions to be closer to the kernel standard.
v2:
* Fixed some spelling errors
---
 config/rte_config.h                            |  3 ---
 doc/guides/prog_guide/kernel_nic_interface.rst | 33 +++++++++++++++++++++++++
 kernel/linux/kni/kni_dev.h                     |  2 +-
 kernel/linux/kni/kni_misc.c                    | 34 ++++++++++++++++++++------
 4 files changed, 60 insertions(+), 12 deletions(-)

diff --git a/config/rte_config.h b/config/rte_config.h
index cab4390..91d96ee 100644
--- a/config/rte_config.h
+++ b/config/rte_config.h
@@ -95,9 +95,6 @@
 #define RTE_SCHED_PORT_N_GRINDERS 8
 #undef RTE_SCHED_VECTOR
 
-/* KNI defines */
-#define RTE_KNI_PREEMPT_DEFAULT 1
-
 /* rte_graph defines */
 #define RTE_GRAPH_BURST_SIZE 256
 #define RTE_LIBRTE_GRAPH_STATS 1
diff --git a/doc/guides/prog_guide/kernel_nic_interface.rst b/doc/guides/prog_guide/kernel_nic_interface.rst
index 1ce03ec..fce3667 100644
--- a/doc/guides/prog_guide/kernel_nic_interface.rst
+++ b/doc/guides/prog_guide/kernel_nic_interface.rst
@@ -56,6 +56,10 @@ can be specified when the module is loaded to control its behavior:
                     off   Interfaces will be created with carrier state set to off.
                     on    Interfaces will be created with carrier state set to on.
                      (charp)
+    parm:           min_scheduling_interval: "Kni thread min scheduling interval (default=100 microseconds):
+                     (long)
+    parm:           max_scheduling_interval: "Kni thread max scheduling interval (default=200 microseconds):
+                     (long)
 
 Loading the ``rte_kni`` kernel module without any optional parameters is
 the typical way a DPDK application gets packets into and out of the kernel
@@ -174,6 +178,35 @@ To set the default carrier state to *off*:
 If the ``carrier`` parameter is not specified, the default carrier state
 of KNI interfaces will be set to *off*.
 
+KNI Kthread Scheduling
+~~~~~~~~~~~~~~~~~~~~~~
+
+The ``min_scheduling_interval`` and ``max_scheduling_interval`` parameters
+control the rescheduling interval of the KNI kthreads.
+
+This might be useful if we have use cases in which we require improved
+latency or performance for control plane traffic.
+
+The implementation is backed by Linux High Precision Timers, and uses ``usleep_range``.
+Hence, it will have the same granularity constraints as this Linux subsystem.
+
+For Linux High Precision Timers, you can check the following resource: `Kernel Timers <http://www.kernel.org/doc/Documentation/timers/timers-howto.txt>`_
+
+To set the ``min_scheduling_interval`` to a value of 100 microseconds:
+
+.. code-block:: console
+
+    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko min_scheduling_interval=100
+
+To set the ``max_scheduling_interval`` to a value of 200 microseconds:
+
+.. code-block:: console
+
+    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko max_scheduling_interval=200
+
+If the ``min_scheduling_interval`` and ``max_scheduling_interval`` parameters are
+not specified, the default interval limits will be set to *100* and *200* respectively.
+
 KNI Creation and Deletion
 -------------------------
 
diff --git a/kernel/linux/kni/kni_dev.h b/kernel/linux/kni/kni_dev.h
index c15da311..bb4d891 100644
--- a/kernel/linux/kni/kni_dev.h
+++ b/kernel/linux/kni/kni_dev.h
@@ -27,7 +27,7 @@
 #include <linux/list.h>
 
 #include <rte_kni_common.h>
-#define KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
+#define KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL 1000000 /* us */
 
 #define MBUF_BURST_SZ 32
 
diff --git a/kernel/linux/kni/kni_misc.c b/kernel/linux/kni/kni_misc.c
index f4944e1..23132bb 100644
--- a/kernel/linux/kni/kni_misc.c
+++ b/kernel/linux/kni/kni_misc.c
@@ -41,6 +41,10 @@ static uint32_t multiple_kthread_on;
 static char *carrier;
 uint32_t kni_dflt_carrier;
 
+/* Kni thread scheduling interval */
+static long min_scheduling_interval = 100; /* us */
+static long max_scheduling_interval = 200; /* us */
+
 #define KNI_DEV_IN_USE_BIT_NUM 0 /* Bit number for device in use */
 
 static int kni_net_id;
@@ -128,11 +132,8 @@ kni_thread_single(void *data)
 			}
 		}
 		up_read(&knet->kni_list_lock);
-#ifdef RTE_KNI_PREEMPT_DEFAULT
 		/* reschedule out for a while */
-		schedule_timeout_interruptible(
-			usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
-#endif
+		usleep_range(min_scheduling_interval, max_scheduling_interval);
 	}
 
 	return 0;
@@ -149,10 +150,7 @@ kni_thread_multiple(void *param)
 			kni_net_rx(dev);
 			kni_net_poll_resp(dev);
 		}
-#ifdef RTE_KNI_PREEMPT_DEFAULT
-		schedule_timeout_interruptible(
-			usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
-#endif
+		usleep_range(min_scheduling_interval, max_scheduling_interval);
 	}
 
 	return 0;
@@ -590,6 +588,14 @@ kni_init(void)
 	else
 		pr_debug("Default carrier state set to on.\n");
 
+	if (min_scheduling_interval < 0 || max_scheduling_interval < 0 ||
+		min_scheduling_interval > KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
+		max_scheduling_interval > KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
+		min_scheduling_interval >= max_scheduling_interval) {
+		pr_err("Invalid parameters for scheduling interval\n");
+		return -EINVAL;
+	}
+
 #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
 	rc = register_pernet_subsys(&kni_net_ops);
 #else
@@ -656,3 +662,15 @@ MODULE_PARM_DESC(carrier,
 "\t\ton    Interfaces will be created with carrier state set to on.\n"
 "\t\t"
 );
+
+module_param(min_scheduling_interval, long, 0644);
+MODULE_PARM_DESC(min_scheduling_interval,
+"\t\tKni thread min scheduling interval (default=100 microseconds):\n"
+"\t\t"
+);
+
+module_param(max_scheduling_interval, long, 0644);
+MODULE_PARM_DESC(max_scheduling_interval,
+"\t\tKni thread max scheduling interval (default=200 microseconds):\n"
+"\t\t"
+);
-- 
2.7.4

RE: [PATCH v4] kni: allow configuring the kni thread granularity

[Connolly, Padraig J]

> -----Original Message-----
> From: Tudor Cornea <tudor.cornea@gmail.com>
> Sent: Wednesday, November 24, 2021 7:24 PM
> To: Yigit, Ferruh <ferruh.yigit@intel.com>
> Cc: thomas@monjalon.net; stephen@networkplumber.org; Zhang, Helin
> <helin.zhang@intel.com>; dev@dpdk.org; Tudor Cornea
> <tudor.cornea@gmail.com>
> Subject: [PATCH v4] kni: allow configuring the kni thread granularity
> 
> The Kni kthreads seem to be re-scheduled at a granularity of roughly
> 1 millisecond right now, which seems to be insufficient for performing tests
> involving a lot of control plane traffic.
> 
> Even if KNI_KTHREAD_RESCHEDULE_INTERVAL is set to 5 microseconds, it
> seems that the existing code cannot reschedule at the desired granularily,
> due to precision constraints of schedule_timeout_interruptible().
> 
> In our use case, we leverage the Linux Kernel for control plane, and it is not
> uncommon to have 60K - 100K pps for some signaling protocols.
> 
> Since we are not in atomic context, the usleep_range() function seems to be
> more appropriate for being able to introduce smaller controlled delays, in the
> range of 5-10 microseconds. Upon reading the existing code, it would seem
> that this was the original intent. Adding sub-millisecond delays, seems
> unfeasible with a call to schedule_timeout_interruptible().
> 
> KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
> schedule_timeout_interruptible(
>         usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
> 
> Below, we attempted a brief comparison between the existing
> implementation, which uses schedule_timeout_interruptible() and
> usleep_range().
> 
> We attempt to measure the CPU usage, and RTT between two Kni interfaces,
> which are created on top of vmxnet3 adapters, connected by a vSwitch.
> 
> insmod rte_kni.ko kthread_mode=single carrier=on
> 
> schedule_timeout_interruptible(usecs_to_jiffies(5))
> kni_single CPU Usage: 2-4 %
> [root@localhost ~]# ping 1.1.1.2 -I eth1 PING 1.1.1.2 (1.1.1.2) from 1.1.1.1
> eth1: 56(84) bytes of data.
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.70 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.00 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.99 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.985 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.00 ms
> 
> usleep_range(5, 10)
> kni_single CPU usage: 50%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.338 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.150 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.123 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.139 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.159 ms
> 
> usleep_range(20, 50)
> kni_single CPU usage: 24%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.202 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.170 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.171 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.248 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.185 ms
> 
> usleep_range(50, 100)
> kni_single CPU usage: 13%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.537 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.257 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.231 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.143 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.200 ms
> 
> usleep_range(100, 200)
> kni_single CPU usage: 7%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.716 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.167 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.459 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.455 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.252 ms
> 
> usleep_range(1000, 1100)
> kni_single CPU usage: 2%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.22 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.15 ms
> 
> Upon testing, usleep_range(1000, 1100) seems roughly equivalent in latency
> and cpu usage to the variant with schedule_timeout_interruptible(), while
> usleep_range(100, 200) seems to give a decent tradeoff between latency
> and cpu usage, while allowing users to tweak the limits for improved
> precision if they have such use cases.
> 
> Disabling RTE_KNI_PREEMPT_DEFAULT, interestingly seems to lead to a
> softlockup on my kernel.
> 
> Kernel panic - not syncing: softlockup: hung tasks
> CPU: 0 PID: 1226 Comm: kni_single Tainted: G        W  O 3.10 #1
>  <IRQ>  [<ffffffff814f84de>] dump_stack+0x19/0x1b  [<ffffffff814f7891>]
> panic+0xcd/0x1e0  [<ffffffff810993b0>] watchdog_timer_fn+0x160/0x160
> [<ffffffff810644b2>] __run_hrtimer.isra.4+0x42/0xd0  [<ffffffff81064b57>]
> hrtimer_interrupt+0xe7/0x1f0  [<ffffffff8102cd57>]
> smp_apic_timer_interrupt+0x67/0xa0
>  [<ffffffff8150321d>] apic_timer_interrupt+0x6d/0x80
> 
> This patch also attempts to remove this option.
> 
> References:
> [1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt
> 
> Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>
> 
> ---
> v4:
> * Removed RTE_KNI_PREEMPT_DEFAULT configuration option
> v3:
> * Fixed unwrapped commit description warning
> * Changed from hrtimers to Linux High Precision Timers in docs
> * Added two tabs at the beginning of the new params description.
>   Stephen correctly pointed out that the descriptions of the parameters
>   for the Kni module are nonstandard w.r.t existing kernel code.
>   I was thinking to preserve compatibility with the existing parameters
>   of the Kni module for the moment, while an additional clean-up patch
>   could format the descriptions to be closer to the kernel standard.
> v2:
> * Fixed some spelling errors
> ---
>  config/rte_config.h                            |  3 ---
>  doc/guides/prog_guide/kernel_nic_interface.rst | 33
> +++++++++++++++++++++++++
>  kernel/linux/kni/kni_dev.h                     |  2 +-
>  kernel/linux/kni/kni_misc.c                    | 34 ++++++++++++++++++++------
>  4 files changed, 60 insertions(+), 12 deletions(-)
> 
> diff --git a/config/rte_config.h b/config/rte_config.h index cab4390..91d96ee
> 100644
> --- a/config/rte_config.h
> +++ b/config/rte_config.h
> @@ -95,9 +95,6 @@
>  #define RTE_SCHED_PORT_N_GRINDERS 8
>  #undef RTE_SCHED_VECTOR
> 
> -/* KNI defines */
> -#define RTE_KNI_PREEMPT_DEFAULT 1
> -
>  /* rte_graph defines */
>  #define RTE_GRAPH_BURST_SIZE 256
>  #define RTE_LIBRTE_GRAPH_STATS 1
> diff --git a/doc/guides/prog_guide/kernel_nic_interface.rst
> b/doc/guides/prog_guide/kernel_nic_interface.rst
> index 1ce03ec..fce3667 100644
> --- a/doc/guides/prog_guide/kernel_nic_interface.rst
> +++ b/doc/guides/prog_guide/kernel_nic_interface.rst
> @@ -56,6 +56,10 @@ can be specified when the module is loaded to control
> its behavior:
>                      off   Interfaces will be created with carrier state set to off.
>                      on    Interfaces will be created with carrier state set to on.
>                       (charp)
> +    parm:           min_scheduling_interval: "Kni thread min scheduling interval
> (default=100 microseconds):
> +                     (long)
> +    parm:           max_scheduling_interval: "Kni thread max scheduling interval
> (default=200 microseconds):
> +                     (long)
> 
>  Loading the ``rte_kni`` kernel module without any optional parameters is
> the typical way a DPDK application gets packets into and out of the kernel
> @@ -174,6 +178,35 @@ To set the default carrier state to *off*:
>  If the ``carrier`` parameter is not specified, the default carrier state  of KNI
> interfaces will be set to *off*.
> 
> +KNI Kthread Scheduling
> +~~~~~~~~~~~~~~~~~~~~~~
> +
> +The ``min_scheduling_interval`` and ``max_scheduling_interval``
> +parameters control the rescheduling interval of the KNI kthreads.
> +
> +This might be useful if we have use cases in which we require improved
> +latency or performance for control plane traffic.
> +
> +The implementation is backed by Linux High Precision Timers, and uses
> ``usleep_range``.
> +Hence, it will have the same granularity constraints as this Linux subsystem.
> +
> +For Linux High Precision Timers, you can check the following resource:
> +`Kernel Timers
> +<http://www.kernel.org/doc/Documentation/timers/timers-howto.txt>`_
> +
> +To set the ``min_scheduling_interval`` to a value of 100 microseconds:
> +
> +.. code-block:: console
> +
> +    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko
> + min_scheduling_interval=100
> +
> +To set the ``max_scheduling_interval`` to a value of 200 microseconds:
> +
> +.. code-block:: console
> +
> +    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko
> + max_scheduling_interval=200
> +
> +If the ``min_scheduling_interval`` and ``max_scheduling_interval``
> +parameters are not specified, the default interval limits will be set to *100*
> and *200* respectively.
> +
>  KNI Creation and Deletion
>  -------------------------
> 
> diff --git a/kernel/linux/kni/kni_dev.h b/kernel/linux/kni/kni_dev.h index
> c15da311..bb4d891 100644
> --- a/kernel/linux/kni/kni_dev.h
> +++ b/kernel/linux/kni/kni_dev.h
> @@ -27,7 +27,7 @@
>  #include <linux/list.h>
> 
>  #include <rte_kni_common.h>
> -#define KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
> +#define KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL 1000000 /* us */
> 
>  #define MBUF_BURST_SZ 32
> 
> diff --git a/kernel/linux/kni/kni_misc.c b/kernel/linux/kni/kni_misc.c index
> f4944e1..23132bb 100644
> --- a/kernel/linux/kni/kni_misc.c
> +++ b/kernel/linux/kni/kni_misc.c
> @@ -41,6 +41,10 @@ static uint32_t multiple_kthread_on;  static char
> *carrier;  uint32_t kni_dflt_carrier;
> 
> +/* Kni thread scheduling interval */
> +static long min_scheduling_interval = 100; /* us */ static long
> +max_scheduling_interval = 200; /* us */
> +
>  #define KNI_DEV_IN_USE_BIT_NUM 0 /* Bit number for device in use */
> 
>  static int kni_net_id;
> @@ -128,11 +132,8 @@ kni_thread_single(void *data)
>  			}
>  		}
>  		up_read(&knet->kni_list_lock);
> -#ifdef RTE_KNI_PREEMPT_DEFAULT
>  		/* reschedule out for a while */
> -		schedule_timeout_interruptible(
> -
> 	usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
> -#endif
> +		usleep_range(min_scheduling_interval,
> max_scheduling_interval);
>  	}
> 
>  	return 0;
> @@ -149,10 +150,7 @@ kni_thread_multiple(void *param)
>  			kni_net_rx(dev);
>  			kni_net_poll_resp(dev);
>  		}
> -#ifdef RTE_KNI_PREEMPT_DEFAULT
> -		schedule_timeout_interruptible(
> -
> 	usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
> -#endif
> +		usleep_range(min_scheduling_interval,
> max_scheduling_interval);
>  	}
> 
>  	return 0;
> @@ -590,6 +588,14 @@ kni_init(void)
>  	else
>  		pr_debug("Default carrier state set to on.\n");
> 
> +	if (min_scheduling_interval < 0 || max_scheduling_interval < 0 ||
> +		min_scheduling_interval >
> KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
> +		max_scheduling_interval >
> KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
> +		min_scheduling_interval >= max_scheduling_interval) {
> +		pr_err("Invalid parameters for scheduling interval\n");
> +		return -EINVAL;
> +	}
> +
>  #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
>  	rc = register_pernet_subsys(&kni_net_ops);
>  #else
> @@ -656,3 +662,15 @@ MODULE_PARM_DESC(carrier,
>  "\t\ton    Interfaces will be created with carrier state set to on.\n"
>  "\t\t"
>  );
> +
> +module_param(min_scheduling_interval, long, 0644);
> +MODULE_PARM_DESC(min_scheduling_interval,
> +"\t\tKni thread min scheduling interval (default=100 microseconds):\n"
> +"\t\t"
> +);
> +
> +module_param(max_scheduling_interval, long, 0644);
> +MODULE_PARM_DESC(max_scheduling_interval,
> +"\t\tKni thread max scheduling interval (default=200 microseconds):\n"
> +"\t\t"
> +);
This patch looks good to me.

Tested with <build_dir>/kernel/linux/kni/rte_kni.ko min_scheduling_interval=20 max_scheduling_interval=50

Results:
KNI Perf before patch was added:
64 bytes from 5.5.5.6: icmp_seq=1 ttl=64 time=4.79 ms
64 bytes from 5.5.5.6: icmp_seq=2 ttl=64 time=2.97 ms
64 bytes from 5.5.5.6: icmp_seq=3 ttl=64 time=1.90 ms
64 bytes from 5.5.5.6: icmp_seq=4 ttl=64 time=7.94 ms
64 bytes from 5.5.5.6: icmp_seq=5 ttl=64 time=6.85 ms
KNI Perf after patch was added (min_scheduling_interval=20 max_scheduling_interval=50):
64 bytes from 5.5.5.6: icmp_seq=1 ttl=64 time=0.106 ms
64 bytes from 5.5.5.6: icmp_seq=2 ttl=64 time=0.055 ms
64 bytes from 5.5.5.6: icmp_seq=3 ttl=64 time=0.059 ms
64 bytes from 5.5.5.6: icmp_seq=4 ttl=64 time=0.056 ms
64 bytes from 5.5.5.6: icmp_seq=5 ttl=64 time=0.061 ms

Acked-by: Padraig Connolly <Padraig.J.Connolly@intel.com>
> --
> 2.7.4

--------------------------------------------------------------
Intel Research and Development Ireland Limited
Registered in Ireland
Registered Office: Collinstown Industrial Park, Leixlip, County Kildare
Registered Number: 308263


This e-mail and any attachments may contain confidential material for the sole
use of the intended recipient(s). Any review or distribution by others is
strictly prohibited. If you are not the intended recipient, please contact the
sender and delete all copies.

Re: [PATCH v4] kni: allow configuring the kni thread granularity

[Ferruh Yigit]

On 11/24/2021 7:24 PM, Tudor Cornea wrote:
> The Kni kthreads seem to be re-scheduled at a granularity of roughly
> 1 millisecond right now, which seems to be insufficient for performing
> tests involving a lot of control plane traffic.
> 
> Even if KNI_KTHREAD_RESCHEDULE_INTERVAL is set to 5 microseconds, it
> seems that the existing code cannot reschedule at the desired granularily,
> due to precision constraints of schedule_timeout_interruptible().
> 
> In our use case, we leverage the Linux Kernel for control plane, and
> it is not uncommon to have 60K - 100K pps for some signaling protocols.
> 
> Since we are not in atomic context, the usleep_range() function seems to be
> more appropriate for being able to introduce smaller controlled delays,
> in the range of 5-10 microseconds. Upon reading the existing code, it would
> seem that this was the original intent. Adding sub-millisecond delays,
> seems unfeasible with a call to schedule_timeout_interruptible().
> 
> KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
> schedule_timeout_interruptible(
>          usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
> 
> Below, we attempted a brief comparison between the existing implementation,
> which uses schedule_timeout_interruptible() and usleep_range().
> 
> We attempt to measure the CPU usage, and RTT between two Kni interfaces,
> which are created on top of vmxnet3 adapters, connected by a vSwitch.
> 
> insmod rte_kni.ko kthread_mode=single carrier=on
> 
> schedule_timeout_interruptible(usecs_to_jiffies(5))
> kni_single CPU Usage: 2-4 %
> [root@localhost ~]# ping 1.1.1.2 -I eth1
> PING 1.1.1.2 (1.1.1.2) from 1.1.1.1 eth1: 56(84) bytes of data.
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.70 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.00 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.99 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.985 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.00 ms
> 
> usleep_range(5, 10)
> kni_single CPU usage: 50%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.338 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.150 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.123 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.139 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.159 ms
> 
> usleep_range(20, 50)
> kni_single CPU usage: 24%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.202 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.170 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.171 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.248 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.185 ms
> 
> usleep_range(50, 100)
> kni_single CPU usage: 13%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.537 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.257 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.231 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.143 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.200 ms
> 
> usleep_range(100, 200)
> kni_single CPU usage: 7%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.716 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.167 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.459 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.455 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.252 ms
> 
> usleep_range(1000, 1100)
> kni_single CPU usage: 2%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.22 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.15 ms
> 
> Upon testing, usleep_range(1000, 1100) seems roughly equivalent in
> latency and cpu usage to the variant with schedule_timeout_interruptible(),
> while usleep_range(100, 200) seems to give a decent tradeoff between
> latency and cpu usage, while allowing users to tweak the limits for
> improved precision if they have such use cases.
> 
> Disabling RTE_KNI_PREEMPT_DEFAULT, interestingly seems to lead to a
> softlockup on my kernel.
> 
> Kernel panic - not syncing: softlockup: hung tasks
> CPU: 0 PID: 1226 Comm: kni_single Tainted: G        W  O 3.10 #1
>   <IRQ>  [<ffffffff814f84de>] dump_stack+0x19/0x1b
>   [<ffffffff814f7891>] panic+0xcd/0x1e0
>   [<ffffffff810993b0>] watchdog_timer_fn+0x160/0x160
>   [<ffffffff810644b2>] __run_hrtimer.isra.4+0x42/0xd0
>   [<ffffffff81064b57>] hrtimer_interrupt+0xe7/0x1f0
>   [<ffffffff8102cd57>] smp_apic_timer_interrupt+0x67/0xa0
>   [<ffffffff8150321d>] apic_timer_interrupt+0x6d/0x80
> 
> This patch also attempts to remove this option.
> 
> References:
> [1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt
> 
> Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>
> 
> ---
> v4:
> * Removed RTE_KNI_PREEMPT_DEFAULT configuration option
> v3:
> * Fixed unwrapped commit description warning
> * Changed from hrtimers to Linux High Precision Timers in docs
> * Added two tabs at the beginning of the new params description.
>    Stephen correctly pointed out that the descriptions of the parameters
>    for the Kni module are nonstandard w.r.t existing kernel code.
>    I was thinking to preserve compatibility with the existing parameters
>    of the Kni module for the moment, while an additional clean-up patch
>    could format the descriptions to be closer to the kernel standard.
> v2:
> * Fixed some spelling errors

Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>

Only it doesn't apply cleanly because of the latest changes in the kni,
can you please rebase it?

Please keep the review tag in the new version after rebase.

[PATCH v5] kni: allow configuring the kni thread granularity

[Tudor Cornea]

The Kni kthreads seem to be re-scheduled at a granularity of roughly
1 millisecond right now, which seems to be insufficient for performing
tests involving a lot of control plane traffic.

Even if KNI_KTHREAD_RESCHEDULE_INTERVAL is set to 5 microseconds, it
seems that the existing code cannot reschedule at the desired granularily,
due to precision constraints of schedule_timeout_interruptible().

In our use case, we leverage the Linux Kernel for control plane, and
it is not uncommon to have 60K - 100K pps for some signaling protocols.

Since we are not in atomic context, the usleep_range() function seems to be
more appropriate for being able to introduce smaller controlled delays,
in the range of 5-10 microseconds. Upon reading the existing code, it would
seem that this was the original intent. Adding sub-millisecond delays,
seems unfeasible with a call to schedule_timeout_interruptible().

KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
schedule_timeout_interruptible(
        usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));

Below, we attempted a brief comparison between the existing implementation,
which uses schedule_timeout_interruptible() and usleep_range().

We attempt to measure the CPU usage, and RTT between two Kni interfaces,
which are created on top of vmxnet3 adapters, connected by a vSwitch.

insmod rte_kni.ko kthread_mode=single carrier=on

schedule_timeout_interruptible(usecs_to_jiffies(5))
kni_single CPU Usage: 2-4 %
[root@localhost ~]# ping 1.1.1.2 -I eth1
PING 1.1.1.2 (1.1.1.2) from 1.1.1.1 eth1: 56(84) bytes of data.
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.70 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.00 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.99 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.985 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.00 ms

usleep_range(5, 10)
kni_single CPU usage: 50%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.338 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.150 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.123 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.139 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.159 ms

usleep_range(20, 50)
kni_single CPU usage: 24%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.202 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.170 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.171 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.248 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.185 ms

usleep_range(50, 100)
kni_single CPU usage: 13%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.537 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.257 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.231 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.143 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.200 ms

usleep_range(100, 200)
kni_single CPU usage: 7%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.716 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.167 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.459 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.455 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.252 ms

usleep_range(1000, 1100)
kni_single CPU usage: 2%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.22 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.15 ms

Upon testing, usleep_range(1000, 1100) seems roughly equivalent in
latency and cpu usage to the variant with schedule_timeout_interruptible(),
while usleep_range(100, 200) seems to give a decent tradeoff between
latency and cpu usage, while allowing users to tweak the limits for
improved precision if they have such use cases.

Disabling RTE_KNI_PREEMPT_DEFAULT, interestingly seems to lead to a
softlockup on my kernel.

Kernel panic - not syncing: softlockup: hung tasks
CPU: 0 PID: 1226 Comm: kni_single Tainted: G        W  O 3.10 #1
 <IRQ>  [<ffffffff814f84de>] dump_stack+0x19/0x1b
 [<ffffffff814f7891>] panic+0xcd/0x1e0
 [<ffffffff810993b0>] watchdog_timer_fn+0x160/0x160
 [<ffffffff810644b2>] __run_hrtimer.isra.4+0x42/0xd0
 [<ffffffff81064b57>] hrtimer_interrupt+0xe7/0x1f0
 [<ffffffff8102cd57>] smp_apic_timer_interrupt+0x67/0xa0
 [<ffffffff8150321d>] apic_timer_interrupt+0x6d/0x80

This patch also attempts to remove this option.

References:
[1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt

Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>
Acked-by: Padraig Connolly <Padraig.J.Connolly@intel.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>
---
v5:
* Rebased the patch on top of the dpdk-next-net branch
v4:
* Removed RTE_KNI_PREEMPT_DEFAULT configuration option
v3:
* Fixed unwrapped commit description warning
* Changed from hrtimers to Linux High Precision Timers in docs
* Added two tabs at the beginning of the new params description.
  Stephen correctly pointed out that the descriptions of the parameters
  for the Kni module are nonstandard w.r.t existing kernel code.
  I was thinking to preserve compatibility with the existing parameters
  of the Kni module for the moment, while an additional clean-up patch
  could format the descriptions to be closer to the kernel standard.
v2:
* Fixed some spelling errors
---
---
 config/rte_config.h                            |  3 ---
 doc/guides/prog_guide/kernel_nic_interface.rst | 33 +++++++++++++++++++++++++
 kernel/linux/kni/kni_dev.h                     |  2 +-
 kernel/linux/kni/kni_misc.c                    | 34 ++++++++++++++++++++------
 4 files changed, 60 insertions(+), 12 deletions(-)

diff --git a/config/rte_config.h b/config/rte_config.h
index cab4390..91d96ee 100644
--- a/config/rte_config.h
+++ b/config/rte_config.h
@@ -95,9 +95,6 @@
 #define RTE_SCHED_PORT_N_GRINDERS 8
 #undef RTE_SCHED_VECTOR
 
-/* KNI defines */
-#define RTE_KNI_PREEMPT_DEFAULT 1
-
 /* rte_graph defines */
 #define RTE_GRAPH_BURST_SIZE 256
 #define RTE_LIBRTE_GRAPH_STATS 1
diff --git a/doc/guides/prog_guide/kernel_nic_interface.rst b/doc/guides/prog_guide/kernel_nic_interface.rst
index 771c7d7..a0763c5 100644
--- a/doc/guides/prog_guide/kernel_nic_interface.rst
+++ b/doc/guides/prog_guide/kernel_nic_interface.rst
@@ -61,6 +61,10 @@ can be specified when the module is loaded to control its behavior:
                     userspace callback and supporting async requests (default=off):
                     on    Enable request processing support for bifurcated drivers.
                      (charp)
+    parm:           min_scheduling_interval: "Kni thread min scheduling interval (default=100 microseconds):
+                     (long)
+    parm:           max_scheduling_interval: "Kni thread max scheduling interval (default=200 microseconds):
+                     (long)
 
 
 Loading the ``rte_kni`` kernel module without any optional parameters is
@@ -202,6 +206,35 @@ Enabling bifurcated device support releases ``rtnl`` lock before calling
 callback and locks it back after callback. Also enables asynchronous request to
 support callbacks that requires rtnl lock to work (interface down).
 
+KNI Kthread Scheduling
+~~~~~~~~~~~~~~~~~~~~~~
+
+The ``min_scheduling_interval`` and ``max_scheduling_interval`` parameters
+control the rescheduling interval of the KNI kthreads.
+
+This might be useful if we have use cases in which we require improved
+latency or performance for control plane traffic.
+
+The implementation is backed by Linux High Precision Timers, and uses ``usleep_range``.
+Hence, it will have the same granularity constraints as this Linux subsystem.
+
+For Linux High Precision Timers, you can check the following resource: `Kernel Timers <http://www.kernel.org/doc/Documentation/timers/timers-howto.txt>`_
+
+To set the ``min_scheduling_interval`` to a value of 100 microseconds:
+
+.. code-block:: console
+
+    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko min_scheduling_interval=100
+
+To set the ``max_scheduling_interval`` to a value of 200 microseconds:
+
+.. code-block:: console
+
+    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko max_scheduling_interval=200
+
+If the ``min_scheduling_interval`` and ``max_scheduling_interval`` parameters are
+not specified, the default interval limits will be set to *100* and *200* respectively.
+
 KNI Creation and Deletion
 -------------------------
 
diff --git a/kernel/linux/kni/kni_dev.h b/kernel/linux/kni/kni_dev.h
index e863348..a2c6d9f 100644
--- a/kernel/linux/kni/kni_dev.h
+++ b/kernel/linux/kni/kni_dev.h
@@ -27,7 +27,7 @@
 #include <linux/list.h>
 
 #include <rte_kni_common.h>
-#define KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
+#define KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL 1000000 /* us */
 
 #define MBUF_BURST_SZ 32
 
diff --git a/kernel/linux/kni/kni_misc.c b/kernel/linux/kni/kni_misc.c
index f10dcd0..c5218d5 100644
--- a/kernel/linux/kni/kni_misc.c
+++ b/kernel/linux/kni/kni_misc.c
@@ -45,6 +45,10 @@ uint32_t kni_dflt_carrier;
 static char *enable_bifurcated;
 uint32_t bifurcated_support;
 
+/* Kni thread scheduling interval */
+static long min_scheduling_interval = 100; /* us */
+static long max_scheduling_interval = 200; /* us */
+
 #define KNI_DEV_IN_USE_BIT_NUM 0 /* Bit number for device in use */
 
 static int kni_net_id;
@@ -132,11 +136,8 @@ kni_thread_single(void *data)
 			}
 		}
 		up_read(&knet->kni_list_lock);
-#ifdef RTE_KNI_PREEMPT_DEFAULT
 		/* reschedule out for a while */
-		schedule_timeout_interruptible(
-			usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
-#endif
+		usleep_range(min_scheduling_interval, max_scheduling_interval);
 	}
 
 	return 0;
@@ -153,10 +154,7 @@ kni_thread_multiple(void *param)
 			kni_net_rx(dev);
 			kni_net_poll_resp(dev);
 		}
-#ifdef RTE_KNI_PREEMPT_DEFAULT
-		schedule_timeout_interruptible(
-			usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
-#endif
+		usleep_range(min_scheduling_interval, max_scheduling_interval);
 	}
 
 	return 0;
@@ -617,6 +615,14 @@ kni_init(void)
 	if (bifurcated_support == 1)
 		pr_debug("bifurcated support is enabled.\n");
 
+	if (min_scheduling_interval < 0 || max_scheduling_interval < 0 ||
+		min_scheduling_interval > KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
+		max_scheduling_interval > KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
+		min_scheduling_interval >= max_scheduling_interval) {
+		pr_err("Invalid parameters for scheduling interval\n");
+		return -EINVAL;
+	}
+
 #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
 	rc = register_pernet_subsys(&kni_net_ops);
 #else
@@ -692,3 +698,15 @@ MODULE_PARM_DESC(enable_bifurcated,
 "\t\ton    Enable request processing support for bifurcated drivers.\n"
 "\t\t"
 );
+
+module_param(min_scheduling_interval, long, 0644);
+MODULE_PARM_DESC(min_scheduling_interval,
+"\t\tKni thread min scheduling interval (default=100 microseconds):\n"
+"\t\t"
+);
+
+module_param(max_scheduling_interval, long, 0644);
+MODULE_PARM_DESC(max_scheduling_interval,
+"\t\tKni thread max scheduling interval (default=200 microseconds):\n"
+"\t\t"
+);
-- 
2.7.4

Re: [PATCH v5] kni: allow configuring the kni thread granularity

[Stephen Hemminger]

On Fri, 14 Jan 2022 17:18:19 +0200
Tudor Cornea <tudor.cornea@gmail.com> wrote:

> +module_param(min_scheduling_interval, long, 0644);
> +MODULE_PARM_DESC(min_scheduling_interval,
> +"\t\tKni thread min scheduling interval (default=100 microseconds):\n"
> +"\t\t"
> +);
> +
> +module_param(max_scheduling_interval, long, 0644);
> +MODULE_PARM_DESC(max_scheduling_interval,
> +"\t\tKni thread max scheduling interval (default=200 microseconds):\n"
> +"\t\t"
> +);

Please don't add more bad module parameter strings.
The KNI author did something no other kernel modules do with tabs
and double spacing, stop this bogus stuff.

Is there any reason you have to use KNI at all.
KNI is broken on many levels and is not fixable.
What about virtio or tap?

Re: [PATCH v5] kni: allow configuring the kni thread granularity

[Ferruh Yigit]

On 1/14/2022 4:24 PM, Stephen Hemminger wrote:
> On Fri, 14 Jan 2022 17:18:19 +0200
> Tudor Cornea <tudor.cornea@gmail.com> wrote:
> 
>> +module_param(min_scheduling_interval, long, 0644);
>> +MODULE_PARM_DESC(min_scheduling_interval,
>> +"\t\tKni thread min scheduling interval (default=100 microseconds):\n"
>> +"\t\t"
>> +);
>> +
>> +module_param(max_scheduling_interval, long, 0644);
>> +MODULE_PARM_DESC(max_scheduling_interval,
>> +"\t\tKni thread max scheduling interval (default=200 microseconds):\n"
>> +"\t\t"
>> +);
> 
> Please don't add more bad module parameter strings.
> The KNI author did something no other kernel modules do with tabs
> and double spacing, stop this bogus stuff.
> 

The patch is good, let's not block it for the module parameter string,
all can be fixed with another patch.

Can you please give a sample what is a common way of it, me or Tudor can
do the patch?

> Is there any reason you have to use KNI at all.
> KNI is broken on many levels and is not fixable.
> What about virtio or tap?

Re: [PATCH v5] kni: allow configuring the kni thread granularity

[Tudor Cornea]

[-- Attachment #1: Type: text/plain, Size: 1645 bytes --]

On Fri, 14 Jan 2022 at 18:44, Ferruh Yigit <ferruh.yigit@intel.com> wrote:

> On 1/14/2022 4:24 PM, Stephen Hemminger wrote:
> > On Fri, 14 Jan 2022 17:18:19 +0200
> > Tudor Cornea <tudor.cornea@gmail.com> wrote:
> >
> >> +module_param(min_scheduling_interval, long, 0644);
> >> +MODULE_PARM_DESC(min_scheduling_interval,
> >> +"\t\tKni thread min scheduling interval (default=100 microseconds):\n"
> >> +"\t\t"
> >> +);
> >> +
> >> +module_param(max_scheduling_interval, long, 0644);
> >> +MODULE_PARM_DESC(max_scheduling_interval,
> >> +"\t\tKni thread max scheduling interval (default=200 microseconds):\n"
> >> +"\t\t"
> >> +);
> >
> > Please don't add more bad module parameter strings.
> > The KNI author did something no other kernel modules do with tabs
> > and double spacing, stop this bogus stuff.
> >
>
> The patch is good, let's not block it for the module parameter string,
> all can be fixed with another patch.
>
> Can you please give a sample what is a common way of it, me or Tudor can
> do the patch?
>
>
I agree that the module parameter string is in non-standard format.
I was planning to send a follow-up patch, which would correct the
description for all of the KNI parameters (including the two new parameters
that the current patch would add) in one shot.


> > Is there any reason you have to use KNI at all.
> > KNI is broken on many levels and is not fixable.
> > What about virtio or tap?
>
>
We've run some tests with tap interfaces and found the performance to not
be good enough for our use.
We're going to experiment with virtio_user in the future. I'm aware that
there is a long term plan to deprecate the KNI.

[-- Attachment #2: Type: text/html, Size: 2556 bytes --]

[PATCH v6] kni: allow configuring the kni thread granularity

[Tudor Cornea]

The Kni kthreads seem to be re-scheduled at a granularity of roughly
1 millisecond right now, which seems to be insufficient for performing
tests involving a lot of control plane traffic.

Even if KNI_KTHREAD_RESCHEDULE_INTERVAL is set to 5 microseconds, it
seems that the existing code cannot reschedule at the desired granularily,
due to precision constraints of schedule_timeout_interruptible().

In our use case, we leverage the Linux Kernel for control plane, and
it is not uncommon to have 60K - 100K pps for some signaling protocols.

Since we are not in atomic context, the usleep_range() function seems to be
more appropriate for being able to introduce smaller controlled delays,
in the range of 5-10 microseconds. Upon reading the existing code, it would
seem that this was the original intent. Adding sub-millisecond delays,
seems unfeasible with a call to schedule_timeout_interruptible().

KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
schedule_timeout_interruptible(
        usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));

Below, we attempted a brief comparison between the existing implementation,
which uses schedule_timeout_interruptible() and usleep_range().

We attempt to measure the CPU usage, and RTT between two Kni interfaces,
which are created on top of vmxnet3 adapters, connected by a vSwitch.

insmod rte_kni.ko kthread_mode=single carrier=on

schedule_timeout_interruptible(usecs_to_jiffies(5))
kni_single CPU Usage: 2-4 %
[root@localhost ~]# ping 1.1.1.2 -I eth1
PING 1.1.1.2 (1.1.1.2) from 1.1.1.1 eth1: 56(84) bytes of data.
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.70 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.00 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.99 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.985 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.00 ms

usleep_range(5, 10)
kni_single CPU usage: 50%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.338 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.150 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.123 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.139 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.159 ms

usleep_range(20, 50)
kni_single CPU usage: 24%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.202 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.170 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.171 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.248 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.185 ms

usleep_range(50, 100)
kni_single CPU usage: 13%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.537 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.257 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.231 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.143 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.200 ms

usleep_range(100, 200)
kni_single CPU usage: 7%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.716 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.167 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.459 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.455 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.252 ms

usleep_range(1000, 1100)
kni_single CPU usage: 2%
64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.22 ms
64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=1.17 ms
64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.15 ms

Upon testing, usleep_range(1000, 1100) seems roughly equivalent in
latency and cpu usage to the variant with schedule_timeout_interruptible(),
while usleep_range(100, 200) seems to give a decent tradeoff between
latency and cpu usage, while allowing users to tweak the limits for
improved precision if they have such use cases.

Disabling RTE_KNI_PREEMPT_DEFAULT, interestingly seems to lead to a
softlockup on my kernel.

Kernel panic - not syncing: softlockup: hung tasks
CPU: 0 PID: 1226 Comm: kni_single Tainted: G        W  O 3.10 #1
 <IRQ>  [<ffffffff814f84de>] dump_stack+0x19/0x1b
 [<ffffffff814f7891>] panic+0xcd/0x1e0
 [<ffffffff810993b0>] watchdog_timer_fn+0x160/0x160
 [<ffffffff810644b2>] __run_hrtimer.isra.4+0x42/0xd0
 [<ffffffff81064b57>] hrtimer_interrupt+0xe7/0x1f0
 [<ffffffff8102cd57>] smp_apic_timer_interrupt+0x67/0xa0
 [<ffffffff8150321d>] apic_timer_interrupt+0x6d/0x80

This patch also attempts to remove this option.

References:
[1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt

Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>
Acked-by: Padraig Connolly <Padraig.J.Connolly@intel.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>
---
v6:
* Removed tabs and newline in the description of the
  min_scheduling_interval and max_scheduling_interval
  parameters. They seem to be non-standard.
  In a quick glance over the Linux tree, I saw some (rare)
  usages of newlines and tabs:
      drivers/scsi/bnx2fc/bnx2fc_fcoe.c (debug_logging)
  Fixing the other parameters might mean that we have to chop
  some text, otherwise the line could probably get too big.
v5:
* Rebased the patch on top of the dpdk-next-net branch
v4:
* Removed RTE_KNI_PREEMPT_DEFAULT configuration option
v3:
* Fixed unwrapped commit description warning
* Changed from hrtimers to Linux High Precision Timers in docs
* Added two tabs at the beginning of the new params description.
  Stephen correctly pointed out that the descriptions of the parameters
  for the Kni module are nonstandard w.r.t existing kernel code.
  I was thinking to preserve compatibility with the existing parameters
  of the Kni module for the moment, while an additional clean-up patch
  could format the descriptions to be closer to the kernel standard.
v2:
* Fixed some spelling errors
---
---
 config/rte_config.h                            |  3 ---
 doc/guides/prog_guide/kernel_nic_interface.rst | 33 ++++++++++++++++++++++++++
 kernel/linux/kni/kni_dev.h                     |  2 +-
 kernel/linux/kni/kni_misc.c                    | 32 ++++++++++++++++++-------
 4 files changed, 58 insertions(+), 12 deletions(-)

diff --git a/config/rte_config.h b/config/rte_config.h
index cab4390..91d96ee 100644
--- a/config/rte_config.h
+++ b/config/rte_config.h
@@ -95,9 +95,6 @@
 #define RTE_SCHED_PORT_N_GRINDERS 8
 #undef RTE_SCHED_VECTOR
 
-/* KNI defines */
-#define RTE_KNI_PREEMPT_DEFAULT 1
-
 /* rte_graph defines */
 #define RTE_GRAPH_BURST_SIZE 256
 #define RTE_LIBRTE_GRAPH_STATS 1
diff --git a/doc/guides/prog_guide/kernel_nic_interface.rst b/doc/guides/prog_guide/kernel_nic_interface.rst
index 771c7d7..a0763c5 100644
--- a/doc/guides/prog_guide/kernel_nic_interface.rst
+++ b/doc/guides/prog_guide/kernel_nic_interface.rst
@@ -61,6 +61,10 @@ can be specified when the module is loaded to control its behavior:
                     userspace callback and supporting async requests (default=off):
                     on    Enable request processing support for bifurcated drivers.
                      (charp)
+    parm:           min_scheduling_interval: "Kni thread min scheduling interval (default=100 microseconds):
+                     (long)
+    parm:           max_scheduling_interval: "Kni thread max scheduling interval (default=200 microseconds):
+                     (long)
 
 
 Loading the ``rte_kni`` kernel module without any optional parameters is
@@ -202,6 +206,35 @@ Enabling bifurcated device support releases ``rtnl`` lock before calling
 callback and locks it back after callback. Also enables asynchronous request to
 support callbacks that requires rtnl lock to work (interface down).
 
+KNI Kthread Scheduling
+~~~~~~~~~~~~~~~~~~~~~~
+
+The ``min_scheduling_interval`` and ``max_scheduling_interval`` parameters
+control the rescheduling interval of the KNI kthreads.
+
+This might be useful if we have use cases in which we require improved
+latency or performance for control plane traffic.
+
+The implementation is backed by Linux High Precision Timers, and uses ``usleep_range``.
+Hence, it will have the same granularity constraints as this Linux subsystem.
+
+For Linux High Precision Timers, you can check the following resource: `Kernel Timers <http://www.kernel.org/doc/Documentation/timers/timers-howto.txt>`_
+
+To set the ``min_scheduling_interval`` to a value of 100 microseconds:
+
+.. code-block:: console
+
+    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko min_scheduling_interval=100
+
+To set the ``max_scheduling_interval`` to a value of 200 microseconds:
+
+.. code-block:: console
+
+    # insmod <build_dir>/kernel/linux/kni/rte_kni.ko max_scheduling_interval=200
+
+If the ``min_scheduling_interval`` and ``max_scheduling_interval`` parameters are
+not specified, the default interval limits will be set to *100* and *200* respectively.
+
 KNI Creation and Deletion
 -------------------------
 
diff --git a/kernel/linux/kni/kni_dev.h b/kernel/linux/kni/kni_dev.h
index e863348..a2c6d9f 100644
--- a/kernel/linux/kni/kni_dev.h
+++ b/kernel/linux/kni/kni_dev.h
@@ -27,7 +27,7 @@
 #include <linux/list.h>
 
 #include <rte_kni_common.h>
-#define KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
+#define KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL 1000000 /* us */
 
 #define MBUF_BURST_SZ 32
 
diff --git a/kernel/linux/kni/kni_misc.c b/kernel/linux/kni/kni_misc.c
index f10dcd0..45ef4c5 100644
--- a/kernel/linux/kni/kni_misc.c
+++ b/kernel/linux/kni/kni_misc.c
@@ -45,6 +45,10 @@ uint32_t kni_dflt_carrier;
 static char *enable_bifurcated;
 uint32_t bifurcated_support;
 
+/* Kni thread scheduling interval */
+static long min_scheduling_interval = 100; /* us */
+static long max_scheduling_interval = 200; /* us */
+
 #define KNI_DEV_IN_USE_BIT_NUM 0 /* Bit number for device in use */
 
 static int kni_net_id;
@@ -132,11 +136,8 @@ kni_thread_single(void *data)
 			}
 		}
 		up_read(&knet->kni_list_lock);
-#ifdef RTE_KNI_PREEMPT_DEFAULT
 		/* reschedule out for a while */
-		schedule_timeout_interruptible(
-			usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
-#endif
+		usleep_range(min_scheduling_interval, max_scheduling_interval);
 	}
 
 	return 0;
@@ -153,10 +154,7 @@ kni_thread_multiple(void *param)
 			kni_net_rx(dev);
 			kni_net_poll_resp(dev);
 		}
-#ifdef RTE_KNI_PREEMPT_DEFAULT
-		schedule_timeout_interruptible(
-			usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
-#endif
+		usleep_range(min_scheduling_interval, max_scheduling_interval);
 	}
 
 	return 0;
@@ -617,6 +615,14 @@ kni_init(void)
 	if (bifurcated_support == 1)
 		pr_debug("bifurcated support is enabled.\n");
 
+	if (min_scheduling_interval < 0 || max_scheduling_interval < 0 ||
+		min_scheduling_interval > KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
+		max_scheduling_interval > KNI_KTHREAD_MAX_RESCHEDULE_INTERVAL ||
+		min_scheduling_interval >= max_scheduling_interval) {
+		pr_err("Invalid parameters for scheduling interval\n");
+		return -EINVAL;
+	}
+
 #ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
 	rc = register_pernet_subsys(&kni_net_ops);
 #else
@@ -692,3 +698,13 @@ MODULE_PARM_DESC(enable_bifurcated,
 "\t\ton    Enable request processing support for bifurcated drivers.\n"
 "\t\t"
 );
+
+module_param(min_scheduling_interval, long, 0644);
+MODULE_PARM_DESC(min_scheduling_interval,
+"Kni thread min scheduling interval (default=100 microseconds)"
+);
+
+module_param(max_scheduling_interval, long, 0644);
+MODULE_PARM_DESC(max_scheduling_interval,
+"Kni thread max scheduling interval (default=200 microseconds)"
+);
-- 
2.7.4

Re: [PATCH v6] kni: allow configuring the kni thread granularity

[Thomas Monjalon]

20/01/2022 13:41, Tudor Cornea:
> The Kni kthreads seem to be re-scheduled at a granularity of roughly
> 1 millisecond right now, which seems to be insufficient for performing
> tests involving a lot of control plane traffic.
> 
> Even if KNI_KTHREAD_RESCHEDULE_INTERVAL is set to 5 microseconds, it
> seems that the existing code cannot reschedule at the desired granularily,
> due to precision constraints of schedule_timeout_interruptible().
> 
> In our use case, we leverage the Linux Kernel for control plane, and
> it is not uncommon to have 60K - 100K pps for some signaling protocols.
> 
> Since we are not in atomic context, the usleep_range() function seems to be
> more appropriate for being able to introduce smaller controlled delays,
> in the range of 5-10 microseconds. Upon reading the existing code, it would
> seem that this was the original intent. Adding sub-millisecond delays,
> seems unfeasible with a call to schedule_timeout_interruptible().
> 
> KNI_KTHREAD_RESCHEDULE_INTERVAL 5 /* us */
> schedule_timeout_interruptible(
>         usecs_to_jiffies(KNI_KTHREAD_RESCHEDULE_INTERVAL));
> 
> Below, we attempted a brief comparison between the existing implementation,
> which uses schedule_timeout_interruptible() and usleep_range().
> 
> We attempt to measure the CPU usage, and RTT between two Kni interfaces,
> which are created on top of vmxnet3 adapters, connected by a vSwitch.
> 
> insmod rte_kni.ko kthread_mode=single carrier=on
> 
> schedule_timeout_interruptible(usecs_to_jiffies(5))
> kni_single CPU Usage: 2-4 %
> [root@localhost ~]# ping 1.1.1.2 -I eth1
> PING 1.1.1.2 (1.1.1.2) from 1.1.1.1 eth1: 56(84) bytes of data.
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.70 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.00 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.99 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.985 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.00 ms
> 
> usleep_range(5, 10)
> kni_single CPU usage: 50%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.338 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.150 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.123 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.139 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.159 ms
> 
> usleep_range(20, 50)
> kni_single CPU usage: 24%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.202 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.170 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.171 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.248 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.185 ms
> 
> usleep_range(50, 100)
> kni_single CPU usage: 13%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.537 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.257 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.231 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.143 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.200 ms
> 
> usleep_range(100, 200)
> kni_single CPU usage: 7%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=0.716 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=0.167 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=0.459 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=0.455 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=0.252 ms
> 
> usleep_range(1000, 1100)
> kni_single CPU usage: 2%
> 64 bytes from 1.1.1.2: icmp_seq=1 ttl=64 time=2.22 ms
> 64 bytes from 1.1.1.2: icmp_seq=2 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=3 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=4 ttl=64 time=1.17 ms
> 64 bytes from 1.1.1.2: icmp_seq=5 ttl=64 time=1.15 ms
> 
> Upon testing, usleep_range(1000, 1100) seems roughly equivalent in
> latency and cpu usage to the variant with schedule_timeout_interruptible(),
> while usleep_range(100, 200) seems to give a decent tradeoff between
> latency and cpu usage, while allowing users to tweak the limits for
> improved precision if they have such use cases.
> 
> Disabling RTE_KNI_PREEMPT_DEFAULT, interestingly seems to lead to a
> softlockup on my kernel.
> 
> Kernel panic - not syncing: softlockup: hung tasks
> CPU: 0 PID: 1226 Comm: kni_single Tainted: G        W  O 3.10 #1
>  <IRQ>  [<ffffffff814f84de>] dump_stack+0x19/0x1b
>  [<ffffffff814f7891>] panic+0xcd/0x1e0
>  [<ffffffff810993b0>] watchdog_timer_fn+0x160/0x160
>  [<ffffffff810644b2>] __run_hrtimer.isra.4+0x42/0xd0
>  [<ffffffff81064b57>] hrtimer_interrupt+0xe7/0x1f0
>  [<ffffffff8102cd57>] smp_apic_timer_interrupt+0x67/0xa0
>  [<ffffffff8150321d>] apic_timer_interrupt+0x6d/0x80
> 
> This patch also attempts to remove this option.
> 
> References:
> [1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt
> 
> Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>
> Acked-by: Padraig Connolly <Padraig.J.Connolly@intel.com>
> Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>
> ---
> v6:
> * Removed tabs and newline in the description of the
> 
>   min_scheduling_interval and max_scheduling_interval
>   parameters. They seem to be non-standard.

The doc had to be updated a bit as well.

Fixed Kni -> KNI and applied, thanks.