rps: avoid one atomic in enqueue_to_backlog

If CONFIG_SMP=y, then we own a queue spinlock, we can avoid the atomic
test_and_set_bit() from napi_schedule_prep().

We now have same number of atomic ops per netif_rx() calls than with
pre-RPS kernel.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 988e42912e72..cdcb9cbedf41 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2432,8 +2432,10 @@ enqueue:
                         return NET_RX_SUCCESS;
                 }
 
-                /* Schedule NAPI for backlog device */
-                if (napi_schedule_prep(&sd->backlog)) {
+                /* Schedule NAPI for backlog device
+                 * We can use non atomic operation since we own the queue lock
+                 */
+                if (!__test_and_set_bit(NAPI_STATE_SCHED, &sd->backlog.state)) {
                         if (!rps_ipi_queued(sd))
                                 ____napi_schedule(sd, &sd->backlog);
                 }