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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 > [] dump_stack+0x19/0x1b > [] panic+0xcd/0x1e0 > [] watchdog_timer_fn+0x160/0x160 > [] __run_hrtimer.isra.4+0x42/0xd0 > [] hrtimer_interrupt+0xe7/0x1f0 > [] smp_apic_timer_interrupt+0x67/0xa0 > [] apic_timer_interrupt+0x6d/0x80 > > References: > [1] https://www.kernel.org/doc/Documentation/timers/timers-howto.txt > > Signed-off-by: Tudor Cornea > <...>