[PATCH 05/15] net: optimize napi_schedule_rps()

[wen.yang@linux.dev]

From: Eric Dumazet <edumazet@google.com>

commit 821eba962d95806beb0440742c4062a9da8a386b upstream.

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>
Signed-off-by: Wen Yang <wen.yang@linux.dev>
---
 net/core/dev.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index a46caebb06f7..10a8883ae490 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4727,8 +4727,6 @@ 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.
@@ -4742,7 +4740,11 @@ 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 */
-- 
2.25.1