Re: [PATCH net-next] sock: avoid dirtying incoming_cpu if not needed

From: Paolo Abeni <pabeni@redhat.com>
Date: Wed, 21 Jun 2017 11:45:31 +0200

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>

Applied.