From: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
Date: Mon, 9 Mar 2020 06:50:59 +0000 (+0100)
Subject: event/dsw: reduce latency in low-load situations
X-Git-Url: http://git.droids-corp.org/?a=commitdiff_plain;h=3db0a0984f42255a0c4c97b80c7ac1ded8f3dd86;p=dpdk.git

event/dsw: reduce latency in low-load situations

In DSW, in case a port can't produce any events for the application to
consume, the port is considered idle.

To slightly reduce wall-time latency, flush the port's output buffer
in case of such an empty dequeue.

Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
---

diff --git a/drivers/event/dsw/dsw_event.c b/drivers/event/dsw/dsw_event.c
index d68b71b982..05abfb24c7 100644
--- a/drivers/event/dsw/dsw_event.c
+++ b/drivers/event/dsw/dsw_event.c
@@ -1242,11 +1242,11 @@ dsw_event_dequeue_burst(void *port, struct rte_event *events, uint16_t num,
 		 * seem to improve performance.
 		 */
 		dsw_port_record_seen_events(port, events, dequeued);
-	}
-	/* XXX: Assuming the port can't produce any more work,
-	 *	consider flushing the output buffer, on dequeued ==
-	 *	0.
-	 */
+	} else /* Zero-size dequeue means a likely idle port, and thus
+		* we can afford trading some efficiency for a slightly
+		* reduced event wall-time latency.
+		*/
+		dsw_port_flush_out_buffers(dsw, port);
 
 #ifdef DSW_SORT_DEQUEUED
 	dsw_stable_sort(events, dequeued, sizeof(events[0]), dsw_cmp_event);