Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <1541264071-9905-1-git-send-email-laoar.shao@gmail.com> <945a90d62aa45c4b53349ba0a104574759d40efe.camel@perches.com>
In-Reply-To: <945a90d62aa45c4b53349ba0a104574759d40efe.camel@perches.com>
From:   Yafang Shao <laoar.shao@gmail.com>
Date:   Sun, 4 Nov 2018 09:27:34 +0800
Message-ID: <CALOAHbB0CQkXfi6Xt-S8u0jQNGpbwFN0aEQz4gxnrYr51Fmd+w@mail.gmail.com>
Subject: Re: [PATCH] tcp: do not update snd_una if it is same with ack_seq
To:     joe@perches.com
Cc:     David Miller <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Sun, Nov 4, 2018 at 1:04 AM Joe Perches <joe@perches.com> wrote:
>
> On Sun, 2018-11-04 at 00:54 +0800, Yafang Shao wrote:
> > In the slow path, TCP_SKB_SB(skb)->ack_seq may be same with tp->snd_una,
> > and under this condition we don't need to update the snd_una.
> >
> > Furthermore, tcp_ack_update_window() is only called in slow path,
> > so introducing this check won't affect the fast path processing.
> []
> > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> []
> > @@ -3610,7 +3611,7 @@ 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) {
>
> stylistic nit:
>
> While the precedence is correct in any case,
> perhaps adding parentheses around
>         flag & FLAG_SND_UNA_ADVANCED
> would make it more obvious.
>

Sure. will change it.

Thanks
Yafang