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sock: avoid dirtying incoming_cpu if not needed

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for connected socket, the incoming_cpu field in the sock struct
is not going to change frequently, but we are setting it
unconditionally for each packet.

Since sk_incoming_cpu and sk_flags share the same cacheline,
and the latter is access by udp_recvmsg(), this cause a cache
miss for each packet for UDP connected socket.

With this patch, we set the incoming cpu field only when the
ingress cpu really changes.

This gives a small but measurable performance improvement for
connected UDP socket.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Paolo Abeni 2017-06-21 11:45:31 +02:00 committed by David S. Miller
parent 28b5ba2aa0
commit 34cfb542b5
1 changed files with 4 additions and 1 deletions
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5
include/net/sock.h
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@ -907,7 +907,10 @@ static inline int sk_backlog_rcv(struct sock *sk, struct sk_buff *skb)
static inline void sk_incoming_cpu_update(struct sock *sk)
{
sk->sk_incoming_cpu = raw_smp_processor_id();
int cpu = raw_smp_processor_id();
if (unlikely(sk->sk_incoming_cpu != cpu))
sk->sk_incoming_cpu = cpu;
}
static inline void sock_rps_record_flow_hash(__u32 hash)