netdev - Re: [PATCH net-next] tcp: tcp_transmit

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Date:	Thu, 10 Oct 2013 08:54:32 -0700
From:	Yuchung Cheng <ycheng@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, MF Nowlan <fitz@...yale.edu>,
	Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net-next] tcp: tcp_transmit_skb() optimizations

On Thu, Oct 10, 2013 at 8:43 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> 1) We need to take a timestamp only for skb that should be cloned.
>
> Other skbs are not in write queue and no rtt estimation is done on them.
>
> 2) the unlikely() hint is wrong for receivers (they send pure ACK)
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: MF Nowlan <fitz@...yale.edu>
> Cc: Yuchung Cheng <ycheng@...gle.com>
> Cc: Neal Cardwell <ncardwell@...gle.com>
Acked-By: Yuchung Cheng <ycheng@...gle.com>
> ---
>  net/ipv4/tcp_output.c |   14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index faec813..c40f608 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -850,15 +850,15 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
>
>         BUG_ON(!skb || !tcp_skb_pcount(skb));
>
> -       /* If congestion control is doing timestamping, we must
> -        * take such a timestamp before we potentially clone/copy.
> -        */
> -       if (icsk->icsk_ca_ops->flags & TCP_CONG_RTT_STAMP)
> -               __net_timestamp(skb);
> -
> -       if (likely(clone_it)) {
> +       if (clone_it) {
>                 const struct sk_buff *fclone = skb + 1;
>
> +               /* If congestion control is doing timestamping, we must
> +                * take such a timestamp before we potentially clone/copy.
> +                */
> +               if (icsk->icsk_ca_ops->flags & TCP_CONG_RTT_STAMP)
> +                       __net_timestamp(skb);
> +
>                 if (unlikely(skb->fclone == SKB_FCLONE_ORIG &&
>                              fclone->fclone == SKB_FCLONE_CLONE))
>                         NET_INC_STATS_BH(sock_net(sk),
>
>
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