diff mbox series

[ovs-dev,v4,15/27] dpif-netdev: Quiesce offload thread periodically

Message ID ff3e6564d17ac154ab5ebdf680772bbbeabff680.1623234822.git.grive@u256.net
State Changes Requested
Headers show
Series [ovs-dev,v4,01/27] ovs-thread: Fix barrier use-after-free | expand

Commit Message

Gaetan Rivet June 9, 2021, 1:09 p.m. UTC 
Similar to what was done for the PMD threads [1], reduce the performance
impact of quiescing too often in the offload thread.

After each processed offload, the offload thread currently quiesce and
will sync with RCU. This synchronization can be lengthy and make the
thread unnecessary slow.

Instead attempt to quiesce every 10 ms at most. While the queue is
empty, the offload thread remains quiescent.

[1]: 81ac8b3b194c ("dpif-netdev: Do RCU synchronization at fixed interval
     in PMD main loop.")

Signed-off-by: Gaetan Rivet <grive@u256.net>
Reviewed-by: Eli Britstein <elibr@nvidia.com>
---
 lib/dpif-netdev.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

Comments

Maxime Coquelin Aug. 27, 2021, 3 p.m. UTC | #1 
On 6/9/21 3:09 PM, Gaetan Rivet wrote:
> Similar to what was done for the PMD threads [1], reduce the performance
> impact of quiescing too often in the offload thread.
> 
> After each processed offload, the offload thread currently quiesce and
> will sync with RCU. This synchronization can be lengthy and make the
> thread unnecessary slow.
> 
> Instead attempt to quiesce every 10 ms at most. While the queue is
> empty, the offload thread remains quiescent.
> 
> [1]: 81ac8b3b194c ("dpif-netdev: Do RCU synchronization at fixed interval
>      in PMD main loop.")
> 
> Signed-off-by: Gaetan Rivet <grive@u256.net>
> Reviewed-by: Eli Britstein <elibr@nvidia.com>
> ---
>  lib/dpif-netdev.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 

Thanks for the fix:

Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Thanks,
Maxime
diff mbox series

Patch

diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index a20eeda4d..e403e461a 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -2740,15 +2740,20 @@  err_free:
     return -1;
 }
 
+#define DP_NETDEV_OFFLOAD_QUIESCE_INTERVAL_US (10 * 1000) /* 10 ms */
+
 static void *
 dp_netdev_flow_offload_main(void *data OVS_UNUSED)
 {
     struct dp_offload_thread_item *offload;
     struct ovs_list *list;
     long long int latency_us;
+    long long int next_rcu;
+    long long int now;
     const char *op;
     int ret;
 
+    next_rcu = time_usec() + DP_NETDEV_OFFLOAD_QUIESCE_INTERVAL_US;
     for (;;) {
         ovs_mutex_lock(&dp_offload_thread.mutex);
         if (ovs_list_is_empty(&dp_offload_thread.list)) {
@@ -2756,6 +2761,7 @@  dp_netdev_flow_offload_main(void *data OVS_UNUSED)
             ovs_mutex_cond_wait(&dp_offload_thread.cond,
                                 &dp_offload_thread.mutex);
             ovsrcu_quiesce_end();
+            next_rcu = time_usec() + DP_NETDEV_OFFLOAD_QUIESCE_INTERVAL_US;
         }
         list = ovs_list_pop_front(&dp_offload_thread.list);
         dp_offload_thread.enqueued_item--;
@@ -2779,7 +2785,9 @@  dp_netdev_flow_offload_main(void *data OVS_UNUSED)
             OVS_NOT_REACHED();
         }
 
-        latency_us = time_usec() - offload->timestamp;
+        now = time_usec();
+
+        latency_us = now - offload->timestamp;
         mov_avg_cma_update(&dp_offload_thread.cma, latency_us);
         mov_avg_ema_update(&dp_offload_thread.ema, latency_us);
 
@@ -2787,7 +2795,12 @@  dp_netdev_flow_offload_main(void *data OVS_UNUSED)
                  ret == 0 ? "succeed" : "failed", op,
                  UUID_ARGS((struct uuid *) &offload->flow->mega_ufid));
         dp_netdev_free_flow_offload(offload);
-        ovsrcu_quiesce();
+
+        /* Do RCU synchronization at fixed interval. */
+        if (now > next_rcu) {
+            ovsrcu_quiesce();
+            next_rcu = time_usec() + DP_NETDEV_OFFLOAD_QUIESCE_INTERVAL_US;
+        }
     }
 
     return NULL;