netdev - [PATCH net-next] udp: prefetch rmem_alloc in udp_queue_rcv

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Message-Id: <ec963336242664e99c2f47f399c621aa7f5e2885.1498033422.git.pabeni@redhat.com>
Date:   Wed, 21 Jun 2017 10:24:40 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>
Subject: [PATCH net-next] udp: prefetch rmem_alloc in udp_queue_rcv_skb()

On UDP packets processing, if the BH is the bottle-neck, it
always sees a cache miss while updating rmem_alloc; try to
avoid it prefetching the value as soon as we have the socket
available.

Performances under flood with multiple NIC rx queues used are
unaffected, but when a single NIC rx queue is in use, this
gives ~10% performance improvement.

Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
 net/ipv4/udp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index f3450f0..067a607 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1949,6 +1949,7 @@ static int udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 		}
 	}

+	prefetch(&sk->sk_rmem_alloc);
 	if (rcu_access_pointer(sk->sk_filter) &&
 	    udp_lib_checksum_complete(skb))
 			goto csum_error;
-- 
2.9.4