netdev - Re: [PATCH v2 net-next 1/3] tcp: use TCP_SKB_CB(skb)->tcp

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Message-ID: <CADVnQykSrxg3NU+F7gwxT+RaLMCtGsPMQhhFg=1EpUsb5to8MQ@mail.gmail.com>
Date:	Mon, 15 Sep 2014 12:13:30 -0400
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Eric Dumazet <edumazet@...gle.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Netdev <netdev@...r.kernel.org>,
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH v2 net-next 1/3] tcp: use TCP_SKB_CB(skb)->tcp_flags in
 input path

On Mon, Sep 15, 2014 at 7:19 AM, Eric Dumazet <edumazet@...gle.com> wrote:
> Input path of TCP do not currently uses TCP_SKB_CB(skb)->tcp_flags,
> which is only used in output path.
>
> tcp_recvmsg(), looks at tcp_hdr(skb)->syn for every skb found in receive queue,
> and its unfortunate because this bit is located in a cache line right before
> the payload.
>
> We can simplify TCP by copying tcp flags into TCP_SKB_CB(skb)->tcp_flags.
>
> This patch does so, and avoids the cache line miss in tcp_recvmsg()
>
> Following patches will
> - allow a segment with FIN being coalesced in tcp_try_coalesce()
> - simplify tcp_collapse() by not copying the headers.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Acked-by: Neal Cardwell <ncardwell@...gle.com>

neal
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