net: add cpu_relax to busy poll loop

Add a cpu_relaxt to sk_busy_loop.

Julie Cummings reported performance issues when hyperthreading is on.
Arjan van de Ven observed that we should have a cpu_relax() in the
busy poll loop.

Reported-by: Julie Cummings <[email protected]>
Signed-off-by: Eliezer Tamir <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

diff --git a/include/net/busy_poll.h b/include/net/busy_poll.h
index 8a358a2c97e6a82cb98dd6b9586133828306f961..829627d7b8460e1739da979a3937056dde92a48e 100644 (file)
--- a/include/net/busy_poll.h
+++ b/include/net/busy_poll.h
@@ -123,6 +123,7 @@ static inline bool sk_busy_loop(struct sock *sk, int nonblock)
                        /* local bh are disabled so it is ok to use _BH */
                        NET_ADD_STATS_BH(sock_net(sk),
                                         LINUX_MIB_BUSYPOLLRXPACKETS, rc);
+               cpu_relax();
 
        } while (!nonblock && skb_queue_empty(&sk->sk_receive_queue) &&
                 !need_resched() && !busy_loop_timeout(end_time));