netdev - [PATCH net-next 2/2] net: revert "Update RFS target at poll for tcp/udp"

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Date:   Wed,  3 Jan 2018 21:47:11 -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 2/2] net: revert "Update RFS target at poll for tcp/udp"

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

On multi-threaded processes, one common architecture is to have
one (or a small number of) threads polling sockets, and a
considerably larger pool of threads reading form and writing to the
sockets. When we set RPS core on tcp_poll() or udp_poll() we essentially
steer all packets of all the polled FDs to one (or small number of)
cores, creaing a bottleneck and/or RPS misprediction.

Another common architecture is to shard FDs among threads pinned
to cores. In such a setting, setting RPS core in tcp_poll() and
udp_poll() is redundant because the RFS core is correctly
set in recvmsg and sendmsg.

Thus, revert the following commit:
c3f1dbaf6e28 ("net: Update RFS target at poll for tcp/udp").

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/tcp.c | 2 --
 net/ipv4/udp.c | 2 --
 2 files changed, 4 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 7ac583a2b9fe..f68cb33d50d1 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -498,8 +498,6 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
 	const struct tcp_sock *tp = tcp_sk(sk);
 	int state;
 
-	sock_rps_record_flow(sk);
-
 	sock_poll_wait(file, sk_sleep(sk), wait);
 
 	state = inet_sk_state_load(sk);
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index e9c0d1e1772e..db72619e07e4 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2490,8 +2490,6 @@ unsigned int udp_poll(struct file *file, struct socket *sock, poll_table *wait)
 	if (!skb_queue_empty(&udp_sk(sk)->reader_queue))
 		mask |= POLLIN | POLLRDNORM;
 
-	sock_rps_record_flow(sk);
-
 	/* Check for false positives due to checksum errors */
 	if ((mask & POLLRDNORM) && !(file->f_flags & O_NONBLOCK) &&
 	    !(sk->sk_shutdown & RCV_SHUTDOWN) && first_packet_length(sk) == -1)
-- 
2.16.0.rc0.223.g4a4ac83678-goog