[dpdk-dev] [PATCH] vdpa/mlx5: fix polling threads scheduling

[Matan Azrad]

When the event mode is with 0 fixed delay, the polling-thread will never
give-up CPU.

So, when multi-polling-threads are active, the context-switch between
them will be managed by the system which may affect latency according to
the time-out decided by the system.

In order to fix multi-devices polling thread scheduling, this patch
forces rescheduling for each CQ poll iteration.

Move the polling thread to SCHED_RR mode with maximum priority to
complete the fairness.

Fixes: 6956a48cabbb ("vdpa/mlx5: set polling mode default delay to zero")

Signed-off-by: Matan Azrad <matan at nvidia.com>
---
 drivers/vdpa/mlx5/mlx5_vdpa_event.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/vdpa/mlx5/mlx5_vdpa_event.c b/drivers/vdpa/mlx5/mlx5_vdpa_event.c
index 0f635ff..86adc86 100644
--- a/drivers/vdpa/mlx5/mlx5_vdpa_event.c
+++ b/drivers/vdpa/mlx5/mlx5_vdpa_event.c
@@ -232,6 +232,9 @@
 	}
 	if (priv->timer_delay_us)
 		usleep(priv->timer_delay_us);
+	else
+		/* Give-up CPU to improve polling threads scheduling. */
+		pthread_yield();
 }
 
 static void *
@@ -500,6 +503,9 @@
 	rte_cpuset_t cpuset;
 	pthread_attr_t attr;
 	char name[16];
+	const struct sched_param sp = {
+		.sched_priority = sched_get_priority_max(SCHED_RR),
+	};
 
 	if (!priv->eventc)
 		/* All virtqs are in poll mode. */
@@ -520,6 +526,16 @@
 			DRV_LOG(ERR, "Failed to set thread affinity.");
 			return -1;
 		}
+		ret = pthread_attr_setschedpolicy(&attr, SCHED_RR);
+		if (ret) {
+			DRV_LOG(ERR, "Failed to set thread sched policy = RR.");
+			return -1;
+		}
+		ret = pthread_attr_setschedparam(&attr, &sp);
+		if (ret) {
+			DRV_LOG(ERR, "Failed to set thread priority.");
+			return -1;
+		}
 		ret = pthread_create(&priv->timer_tid, &attr,
 				     mlx5_vdpa_poll_handle, (void *)priv);
 		if (ret) {
-- 
1.8.3.1