netdev - Re: [PATCH net-next] sock: avoid dirtying incoming

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Message-Id: <20170621.114435.1437675833962204147.davem@davemloft.net>
Date:   Wed, 21 Jun 2017 11:44:35 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     pabeni@...hat.com
Cc:     netdev@...r.kernel.org, edumazet@...gle.com
Subject: Re: [PATCH net-next] sock: avoid dirtying incoming_cpu if not
 needed

From: Paolo Abeni <pabeni@...hat.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@...hat.com>

Applied.