netdev - [PATCH net-next 3/4] net: optimize napi_schedule

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Message-ID: <20230328235021.1048163-4-edumazet@google.com>
Date:   Tue, 28 Mar 2023 23:50:20 +0000
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     Jason Xing <kernelxing@...cent.com>, netdev@...r.kernel.org,
        eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 3/4] 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@...gle.com>
Cc: Jason Xing <kernelxing@...cent.com>
---
 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 15331edbacf4ca59aa5772c29e95cacd3c106e3f..f34ce93f2f02e7ec71f5e84d449fa99b7a882f0c 100644
--- 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 */
-- 
2.40.0.348.gf938b09366-goog