netdev - [PATCH net-next 1/2] ip: do not set RFS core on error queue reads

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Message-Id: <20180104024711.257600-1-soheil.kdev@gmail.com>
Date:   Wed,  3 Jan 2018 21:47:10 -0500
From:   Soheil Hassas Yeganeh <soheil.kdev@...il.com>
To:     davem@...emloft.net, netdev@...r.kernel.org
Cc:     pjt@...gle.com, ycheng@...gle.com,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: [PATCH net-next 1/2] ip: do not set RFS core on error queue reads

From: Soheil Hassas Yeganeh <soheil@...gle.com>

We should only record RPS on normal reads and writes.
In single threaded processes, all calls record the same state. In
multi-threaded processes where a separate thread processes
errors, the RFS table mispredicts.

Note that, when CONFIG_RPS is disabled, sock_rps_record_flow
is a noop and no branch is added as a result of this patch.

Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com>
Signed-off-by: Willem de Bruijn <willemb@...gle.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
---
 net/ipv4/af_inet.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index bab98a4fedad..54cccdd8b1e3 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -790,7 +790,8 @@ int inet_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
 	int addr_len = 0;
 	int err;
 
-	sock_rps_record_flow(sk);
+	if (likely(!(flags & MSG_ERRQUEUE)))
+		sock_rps_record_flow(sk);
 
 	err = sk->sk_prot->recvmsg(sk, msg, size, flags & MSG_DONTWAIT,
 				   flags & ~MSG_DONTWAIT, &addr_len);
-- 
2.16.0.rc0.223.g4a4ac83678-goog