netdev - [PATCH v2 net-next 04/10] net: avoid dirtying sk->sk_rx_queue

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Message-Id: <20211025164825.259415-5-eric.dumazet@gmail.com>
Date:   Mon, 25 Oct 2021 09:48:19 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: [PATCH v2 net-next 04/10] net: avoid dirtying sk->sk_rx_queue_mapping

From: Eric Dumazet <edumazet@...gle.com>

sk_rx_queue_mapping is located in a cache line that should be kept read mostly.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>
---
 include/net/sock.h | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 99c4194cb61add848e3a35db0f952c4193f5ea1f..b4d3744b188ad869b4ec55f78e04236b710898de 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1916,10 +1916,8 @@ static inline void sk_rx_queue_set(struct sock *sk, const struct sk_buff *skb)
 	if (skb_rx_queue_recorded(skb)) {
 		u16 rx_queue = skb_get_rx_queue(skb);
 
-		if (WARN_ON_ONCE(rx_queue == NO_QUEUE_MAPPING))
-			return;
-
-		sk->sk_rx_queue_mapping = rx_queue;
+		if (unlikely(READ_ONCE(sk->sk_rx_queue_mapping) != rx_queue))
+			WRITE_ONCE(sk->sk_rx_queue_mapping, rx_queue);
 	}
 #endif
 }
-- 
2.33.0.1079.g6e70778dc9-goog