RE: [EXTERNAL] Re: [PATCH v2 1/3] eventdev: introduce event pre-scheduling

[Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com>]

> On 2024-09-19 15:13, Pavan Nikhilesh Bhagavatula wrote:
> >>> From: pbhagavatula@marvell.com <pbhagavatula@marvell.com>
> >>> Sent: Tuesday, September 17, 2024 3:11 AM
> >>> To: jerinj@marvell.com; sthotton@marvell.com; Sevincer, Abdullah
> >>> <abdullah.sevincer@intel.com>; hemant.agrawal@nxp.com;
> >>> sachin.saxena@oss.nxp.com; Van Haaren, Harry
> >> <harry.van.haaren@intel.com>;
> >>> mattias.ronnblom@ericsson.com; liangma@liangbit.com; Mccarthy, Peter
> >>> <peter.mccarthy@intel.com>
> >>> Cc: dev@dpdk.org; Pavan Nikhilesh <pbhagavatula@marvell.com>
> >>> Subject: [PATCH v2 1/3] eventdev: introduce event pre-scheduling
> >>>
> >>> From: Pavan Nikhilesh <pbhagavatula@marvell.com>
> >>>
> >>> Event pre-scheduling improves scheduling performance by assigning
> events
> >> to
> >>> event ports in advance when dequeues are issued.
> >>> The dequeue operation initiates the pre-schedule operation, which
> >> completes in
> >>> parallel without affecting the dequeued event flow contexts and dequeue
> >>> latency.
> >>>
> >> Is the prescheduling done to get the event more quickly in the next
> dequeue?
> >> The first dequeue executes pre-schedule to make events available for the
> next
> >> dequeue.
> >> Is this how it is supposed to work?
> >>
> >
> > Yes, that is correct.
> >
> 
> "improves scheduling performance" may be a bit misleading, in that case.
> I suggest "reduces scheduling overhead" instead. You can argue it likely
> reduces scheduling performance, in certain scenarios. "reduces
> scheduling overhead, at the cost of load balancing performance."
> 

In case of OCTEON, we see double the scheduling performance with
prescheduling without effecting any priority/weight aspects.

> It seems to me that this should be a simple hint-type API, where the
> hint is used by the event device to decide if pre-scheduling should be
> used or not (assuming pre-scheduling on/off is even an option). The hint
> would just be a way for the application to express whether or not it
> want the scheduler to prioritize load balancing agility and port-to-port
> wall-time latency, or scheduling overhead, which in turn could
> potentially be rephrased as the app being throughput or latency/RT-oriented.
> 

The three prescheduling types are designed based on real world use-cases
that some of our customers require in their applications.
Relying on application to provide hits might not be possible in all the cases
as it is very timing sensitive.


> It could also be useful for the event device to know which priority
> levels are to be considered latency-sensitive, and which are
> throughput-oriented - maybe in the form of a threshold.
> 
> >>> Event devices can indicate pre-scheduling capabilities using
> >>> `RTE_EVENT_DEV_CAP_EVENT_PRESCHEDULE` and
> >>> `RTE_EVENT_DEV_CAP_EVENT_PRESCHEDULE_ADAPTIVE` via the event
> >> device
> >>> info function `info.event_dev_cap`.
> >>>
> >>> Applications can select the pre-schedule type and configure it through
> >>> `rte_event_dev_config.preschedule_type` during
> `rte_event_dev_configure`.
> >>>
> >>> The supported pre-schedule types are:
> >>>   * `RTE_EVENT_DEV_PRESCHEDULE_NONE` - No pre-scheduling.
> >>>   * `RTE_EVENT_DEV_PRESCHEDULE` - Always issue a pre-schedule on
> >> dequeue.
> >>>   * `RTE_EVENT_DEV_PRESCHEDULE_ADAPTIVE` - Delay issuing pre-
> schedule
> >>> until
> >>>     there are no forward progress constraints with the held flow contexts.
> >>>
> >>> Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
> >>> ---
> >>>   app/test/test_eventdev.c                    | 63 +++++++++++++++++++++
> >>>   doc/guides/prog_guide/eventdev/eventdev.rst | 22 +++++++
> >>>   lib/eventdev/rte_eventdev.h                 | 48 ++++++++++++++++
> >>>   3 files changed, 133 insertions(+)
> >>>
> >>> diff --git a/app/test/test_eventdev.c b/app/test/test_eventdev.c index
> >>> e4e234dc98..cf496ee88d 100644
> >>> --- a/app/test/test_eventdev.c
> >>> +++ b/app/test/test_eventdev.c
> >>> @@ -1250,6 +1250,67 @@ test_eventdev_profile_switch(void)
> >>>   	return TEST_SUCCESS;
> >>>   }
> >>>
> >>> +static int
> >>> +preschedule_test(rte_event_dev_preschedule_type_t preschedule_type,
> >>> +const char *preschedule_name) {
> >>> +#define NB_EVENTS     1024
> >>> +	uint64_t start, total;
> >>> +	struct rte_event ev;
> >>> +	int rc, cnt;
> >>> +
> >>> +	ev.event_type = RTE_EVENT_TYPE_CPU;
> >>> +	ev.queue_id = 0;
> >>> +	ev.op = RTE_EVENT_OP_NEW;
> >>> +	ev.u64 = 0xBADF00D0;
> >>> +
> >>> +	for (cnt = 0; cnt < NB_EVENTS; cnt++) {
> >>> +		ev.flow_id = cnt;
> >>> +		rc = rte_event_enqueue_burst(TEST_DEV_ID, 0, &ev, 1);
> >>> +		TEST_ASSERT(rc == 1, "Failed to enqueue event");
> >>> +	}
> >>> +
> >>> +	RTE_SET_USED(preschedule_type);
> >>> +	total = 0;
> >>> +	while (cnt) {
> >>> +		start = rte_rdtsc_precise();
> >>> +		rc = rte_event_dequeue_burst(TEST_DEV_ID, 0, &ev, 1, 0);
> >>> +		if (rc) {
> >>> +			total += rte_rdtsc_precise() - start;
> >>> +			cnt--;
> >>> +		}
> >>> +	}
> >>> +	printf("Preschedule type : %s, avg cycles %" PRIu64 "\n",
> >>> preschedule_name,
> >>> +	       total / NB_EVENTS);
> >>> +
> >>> +	return TEST_SUCCESS;
> >>> +}
> >>> +
> >>> +static int
> >>> +test_eventdev_preschedule_configure(void)
> >>> +{
> >>> +	struct rte_event_dev_config dev_conf;
> >>> +	struct rte_event_dev_info info;
> >>> +	int rc;
> >>> +
> >>> +	rte_event_dev_info_get(TEST_DEV_ID, &info);
> >>> +
> >>> +	if ((info.event_dev_cap &
> >> RTE_EVENT_DEV_CAP_EVENT_PRESCHEDULE)
> >>> == 0)
> >>> +		return TEST_SKIPPED;
> >>> +
> >>> +	devconf_set_default_sane_values(&dev_conf, &info);
> >>> +	dev_conf.preschedule_type = RTE_EVENT_DEV_PRESCHEDULE;
> >>> +	rc = rte_event_dev_configure(TEST_DEV_ID, &dev_conf);
> >>> +	TEST_ASSERT_SUCCESS(rc, "Failed to configure eventdev");
> >>> +
> >>> +	rc = preschedule_test(RTE_EVENT_DEV_PRESCHEDULE_NONE,
> >>> "RTE_EVENT_DEV_PRESCHEDULE_NONE");
> >>> +	rc |= preschedule_test(RTE_EVENT_DEV_PRESCHEDULE,
> >>> "RTE_EVENT_DEV_PRESCHEDULE");
> >>> +	if (info.event_dev_cap &
> >>> RTE_EVENT_DEV_CAP_EVENT_PRESCHEDULE_ADAPTIVE)
> >>> +		rc |=
> >>> preschedule_test(RTE_EVENT_DEV_PRESCHEDULE_ADAPTIVE,
> >>> +
> >>> "RTE_EVENT_DEV_PRESCHEDULE_ADAPTIVE");
> >>> +
> >>> +	return rc;
> >>> +}
> >>> +
> >>>   static int
> >>>   test_eventdev_close(void)
> >>>   {
> >>> @@ -1310,6 +1371,8 @@ static struct unit_test_suite
> >>> eventdev_common_testsuite  = {
> >>>   			test_eventdev_start_stop),
> >>>   		TEST_CASE_ST(eventdev_configure_setup,
> >>> eventdev_stop_device,
> >>>   			test_eventdev_profile_switch),
> >>> +		TEST_CASE_ST(eventdev_configure_setup, NULL,
> >>> +			test_eventdev_preschedule_configure),
> >>>   		TEST_CASE_ST(eventdev_setup_device,
> >> eventdev_stop_device,
> >>>   			test_eventdev_link),
> >>>   		TEST_CASE_ST(eventdev_setup_device,
> >> eventdev_stop_device,
> >>> diff --git a/doc/guides/prog_guide/eventdev/eventdev.rst
> >>> b/doc/guides/prog_guide/eventdev/eventdev.rst
> >>> index fb6dfce102..341b9bb2c6 100644
> >>> --- a/doc/guides/prog_guide/eventdev/eventdev.rst
> >>> +++ b/doc/guides/prog_guide/eventdev/eventdev.rst
> >>> @@ -357,6 +357,28 @@ Worker path:
> >>>          // Process the event received.
> >>>      }
> >>>
> >>> +Event Pre-scheduling
> >>> +~~~~~~~~~~~~~~~~~~~~
> >>> +
> >>> +Event pre-scheduling improves scheduling performance by assigning
> >>> +events to event ports in advance when dequeues are issued.
> >>> +The `rte_event_dequeue_burst` operation initiates the pre-schedule
> >>> +operation, which completes in parallel without affecting the dequeued
> >> event
> >>> flow contexts and dequeue latency.
> >>> +On the next dequeue operation, the pre-scheduled events are dequeued
> >>> +and pre-schedule is initiated again.
> >>> +
> >>> +An application can use event pre-scheduling if the event device
> >>> +supports it at either device level or at a individual port level.
> >>> +The application can check pre-schedule capability by checking if
> >>> +``rte_event_dev_info.event_dev_cap``
> >>> +has the bit ``RTE_EVENT_DEV_CAP_PRESCHEDULE`` set, if present
> >>> +pre-scheduling can be enabled at device configuration time by setting
> >>> appropriate pre-schedule type in ``rte_event_dev_config.preschedule``.
> >>> +
> >>> +Currently, the following pre-schedule types are supported:
> >>> + * ``RTE_EVENT_DEV_PRESCHEDULE_NONE`` - No pre-scheduling.
> >>> + * ``RTE_EVENT_DEV_PRESCHEDULE`` - Always issue a pre-schedule when
> >>> dequeue is issued.
> >>> + * ``RTE_EVENT_DEV_PRESCHEDULE_ADAPTIVE`` - Issue pre-schedule
> when
> >>> dequeue is issued and there are
> >>> +   no forward progress constraints.
> >>> +
> >>>   Starting the EventDev
> >>>   ~~~~~~~~~~~~~~~~~~~~~
> >>>
> >>> diff --git a/lib/eventdev/rte_eventdev.h b/lib/eventdev/rte_eventdev.h
> >> index
> >>> 08e5f9320b..5ea7f5a07b 100644
> >>> --- a/lib/eventdev/rte_eventdev.h
> >>> +++ b/lib/eventdev/rte_eventdev.h
> >>> @@ -446,6 +446,30 @@ struct rte_event;
> >>>    * @see RTE_SCHED_TYPE_PARALLEL
> >>>    */
> >>>
> >>> +#define RTE_EVENT_DEV_CAP_EVENT_PRESCHEDULE (1ULL << 16) /**<
> >> Event
> >>> +device supports event pre-scheduling.
> >>> + *
> >>> + * When this capability is available, the application can enable event
> >>> +pre-scheduling on the event
> >>> + * device to pre-schedule events to a event port when
> >>> +`rte_event_dequeue_burst()`
> >>> + * is issued.
> >>> + * The pre-schedule process starts with the `rte_event_dequeue_burst()`
> >>> +call and the
> >>> + * pre-scheduled events are returned on the next
> >> `rte_event_dequeue_burst()`
> >>> call.
> >>> + *
> >>> + * @see rte_event_dev_configure()
> >>> + */
> >>> +
> >>> +#define RTE_EVENT_DEV_CAP_EVENT_PRESCHEDULE_ADAPTIVE (1ULL
> <<
> >> 17)
> >>> /**<
> >>> +Event device supports adaptive event pre-scheduling.
> >>> + *
> >>> + * When this capability is available, the application can enable
> >>> +adaptive pre-scheduling
> >>> + * on the event device where the events are pre-scheduled when there
> >>> +are no forward
> >>> + * progress constraints with the currently held flow contexts.
> >>> + * The pre-schedule process starts with the `rte_event_dequeue_burst()`
> >>> +call and the
> >>> + * pre-scheduled events are returned on the next
> >> `rte_event_dequeue_burst()`
> >>> call.
> >>> + *
> >>> + * @see rte_event_dev_configure()
> >>> + */
> >>> +
> >>>   /* Event device priority levels */
> >>>   #define RTE_EVENT_DEV_PRIORITY_HIGHEST   0
> >>>   /**< Highest priority level for events and queues.
> >>> @@ -680,6 +704,25 @@ rte_event_dev_attr_get(uint8_t dev_id,
> uint32_t
> >>> attr_id,
> >>>    *  @see rte_event_dequeue_timeout_ticks(),
> rte_event_dequeue_burst()
> >>>    */
> >>>
> >>> +typedef enum {
> >>> +	RTE_EVENT_DEV_PRESCHEDULE_NONE = 0,
> >>> +	/* Disable pre-schedule across the event device or on a given event
> >> port.
> >>> +	 * @ref rte_event_dev_config.preschedule_type
> >>> +	 */
> >>> +	RTE_EVENT_DEV_PRESCHEDULE,
> >>> +	/* Enable pre-schedule always across the event device or a given event
> >>> port.
> >>> +	 * @ref rte_event_dev_config.preschedule_type
> >>> +	 * @see RTE_EVENT_DEV_CAP_EVENT_PRESCHEDULE
> >>> +	 */
> >>> +	RTE_EVENT_DEV_PRESCHEDULE_ADAPTIVE,
> >>> +	/* Enable adaptive pre-schedule across the event device or a given
> >> event
> >>> port.
> >>> +	 * Delay issuing pre-schedule until there are no forward progress
> >>> constraints with
> >>> +	 * the held flow contexts.
> >>> +	 * @ref rte_event_dev_config.preschedule_type
> >>> +	 * @see RTE_EVENT_DEV_CAP_EVENT_PRESCHEDULE_ADAPTIVE
> >>> +	 */
> >>> +} rte_event_dev_preschedule_type_t;
> >>> +
> >>>   /** Event device configuration structure */  struct rte_event_dev_config {
> >>>   	uint32_t dequeue_timeout_ns;
> >>> @@ -752,6 +795,11 @@ struct rte_event_dev_config {
> >>>   	 * optimized for single-link usage, this field is a hint for how many
> >>>   	 * to allocate; otherwise, regular event ports and queues will be used.
> >>>   	 */
> >>> +	rte_event_dev_preschedule_type_t preschedule_type;
> >>> +	/**< Event pre-schedule type to use across the event device, if
> >>> supported.
> >>> +	 * @see RTE_EVENT_DEV_CAP_EVENT_PRESCHEDULE
> >>> +	 * @see RTE_EVENT_DEV_CAP_EVENT_PRESCHEDULE_ADAPTIVE
> >>> +	 */
> >>>   };
> >>>
> >>>   /**
> >>> --
> >>> 2.25.1
> >