netdev - [PATCH net-next 3/9] net: avoid dirtying sk->sk_napi

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Message-Id: <20211021162253.333616-6-eric.dumazet@gmail.com>
Date:   Thu, 21 Oct 2021 09:22:47 -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 net-next 3/9] net: avoid dirtying sk->sk_napi_id

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

sk_napi_id is located in a cache line that can be kept read mostly.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/busy_poll.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/net/busy_poll.h b/include/net/busy_poll.h
index 40296ed976a9778ceb239b99ad783cb99b8b92ef..4202c609bb0b09345c0f1c5105adf409a3a89f74 100644
--- a/include/net/busy_poll.h
+++ b/include/net/busy_poll.h
@@ -130,7 +130,8 @@ static inline void skb_mark_napi_id(struct sk_buff *skb,
 static inline void sk_mark_napi_id(struct sock *sk, const struct sk_buff *skb)
 {
 #ifdef CONFIG_NET_RX_BUSY_POLL
-	WRITE_ONCE(sk->sk_napi_id, skb->napi_id);
+	if (unlikely(READ_ONCE(sk->sk_napi_id) != skb->napi_id))
+		WRITE_ONCE(sk->sk_napi_id, skb->napi_id);
 #endif
 	sk_rx_queue_set(sk, skb);
 }
-- 
2.33.0.1079.g6e70778dc9-goog