net: optimize napi_schedule_rps()

Based on initial patch from Jason Xing.

Idea is to not raise NET_RX_SOFTIRQ from napi_schedule_rps()
when we queued a packet into another cpu backlog.

We can do this only in the context of us being called indirectly
from net_rx_action(), to have the guarantee our rps_ipi_list
will be processed before we exit from net_rx_action().

Link: https://lore.kernel.org/lkml/20230325152417.5403-1-kerneljasonxing@gmail.com/
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Tested-by: Jason Xing <kerneljasonxing@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/core/dev.c b/net/core/dev.c
index 15331edbacf4ca59aa5772c29e95cacd3c106e3f..f34ce93f2f02e7ec71f5e84d449fa99b7a882f0c 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4587,8 +4587,6 @@ static void trigger_rx_softirq(void *data)
  *
  * - If this is another cpu queue, link it to our rps_ipi_list,
  *   and make sure we will process rps_ipi_list from net_rx_action().
- *   As we do not know yet if we are called from net_rx_action(),
- *   we have to raise NET_RX_SOFTIRQ. This might change in the future.
  *
  * - If this is our own queue, NAPI schedule our backlog.
  *   Note that this also raises NET_RX_SOFTIRQ.
@@ -4602,7 +4600,11 @@ static void napi_schedule_rps(struct softnet_data *sd)
                sd->rps_ipi_next = mysd->rps_ipi_list;
                mysd->rps_ipi_list = sd;
 
-               __raise_softirq_irqoff(NET_RX_SOFTIRQ);
+               /* If not called from net_rx_action()
+                * we have to raise NET_RX_SOFTIRQ.
+                */
+               if (!mysd->in_net_rx_action)
+                       __raise_softirq_irqoff(NET_RX_SOFTIRQ);
                return;
        }
 #endif /* CONFIG_RPS */