vdpa/mlx5: fix polling threads scheduling

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@nvidia.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Xueming Li <xuemingl@nvidia.com>

diff --git a/drivers/vdpa/mlx5/mlx5_vdpa_event.c b/drivers/vdpa/mlx5/mlx5_vdpa_event.c
index 0f635ff..86adc86 100644 (file)
--- a/drivers/vdpa/mlx5/mlx5_vdpa_event.c
+++ b/drivers/vdpa/mlx5/mlx5_vdpa_event.c
@@ -232,6 +232,9 @@ mlx5_vdpa_timer_sleep(struct mlx5_vdpa_priv *priv, uint32_t max)
        }
        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 @@ mlx5_vdpa_cqe_event_setup(struct mlx5_vdpa_priv *priv)
        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 @@ mlx5_vdpa_cqe_event_setup(struct mlx5_vdpa_priv *priv)
                        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) {