linux-kernel - Re: [PATCH net-next] tcp: minor optimization in tcp ack fast path processing

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Message-ID: <CALOAHbAUoWgBKSKT+vb6CaxGaUkdxvgKXHGAJNZ9G8hiWezqRQ@mail.gmail.com>
Date:   Thu, 8 Nov 2018 09:45:42 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Joe Perches <joe@...ches.com>
Subject: Re: [PATCH net-next] tcp: minor optimization in tcp ack fast path processing

On Wed, Nov 7, 2018 at 11:16 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>
>
> On 11/07/2018 03:20 AM, Yafang Shao wrote:
> > Bitwise operation is a little faster.
>
>
> > So I replace after() with (flag & FLAG_SND_UNA_ADVANCED) as this flag is
> > already set before.
> >
> > Cc: Joe Perches <joe@...ches.com>
> > Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> > ---
> >  net/ipv4/tcp_input.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> > index 2868ef2..0167015 100644
> > --- a/net/ipv4/tcp_input.c
> > +++ b/net/ipv4/tcp_input.c
> > @@ -3610,7 +3610,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
> >       if (flag & FLAG_UPDATE_TS_RECENT)
> >               tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
> >
> > -     if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
> > +     if (!(flag & FLAG_SLOWPATH) && (flag & FLAG_SND_UNA_ADVANCED)) {
> >               /* Window is constant, pure forward advance.
> >                * No more checks are required.
> >                * Note, we use the fact that SND.UNA>=SND.WL2.
> >
>
> What about reducing this to a single conditional jump ?
>
> if ((flag & (FLAG_SLOWPATH | FLAG_SND_UNA_ADVANCED)) == FLAG_SND_UNA_ADVANCED)  {
>

That's better.
Will change it.


Thanks
Yafang