[dpdk-dev] [PATCH] event/sw: perform partial burst enqueues

[Gage Eads <gage.eads@intel.com>]

Previously, the sw event adapter would enqueue either all or no events,
depending on if enough inflight credits were available for the new events
in the burst. If a port is enqueueing a large burst (i.e. a multiple of the
credit update quanta), this can result in suboptimal performance, and
requires an understanding of the sw PMD implementation (in particular, its
credit scheme) to tune an application's burst size.

This affects software that enqueues large bursts of new events, such as the
ethernet event adapter which uses a 128-deep event buffer, when the input
packet rate is sufficiently high.

This change makes the sw PMD enqueue as many events as it has credits, if
there are any new events in the burst.

Signed-off-by: Gage Eads <gage.eads@intel.com>
---
 drivers/event/sw/sw_evdev_worker.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/event/sw/sw_evdev_worker.c b/drivers/event/sw/sw_evdev_worker.c
index 67151f7..063b919 100644
--- a/drivers/event/sw/sw_evdev_worker.c
+++ b/drivers/event/sw/sw_evdev_worker.c
@@ -77,8 +77,10 @@ sw_event_enqueue_burst(void *port, const struct rte_event ev[], uint16_t num)
 		rte_atomic32_add(&sw->inflights, credit_update_quanta);
 		p->inflight_credits += (credit_update_quanta);
 
-		if (p->inflight_credits < new)
-			return 0;
+		/* If there are fewer inflight credits than new events, limit
+		 * the number of enqueued events.
+		 */
+		num = (p->inflight_credits < new) ? p->inflight_credits : new;
 	}
 
 	for (i = 0; i < num; i++) {
-- 
2.7.4