netdev - Re: [PATCH v3] tcp: fix tp->undo_retrans accounting in tcp_sacktag

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Date:   Mon, 13 Sep 2021 12:27:43 -0400
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Yuchung Cheng <ycheng@...gle.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        zhenggy <zhenggy@...natelecom.cn>,
        netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>, qitiepeng@...natelecom.cn,
        wujianguo@...natelecom.cn, liyonglong@...natelecom.cn
Subject: Re: [PATCH v3] tcp: fix tp->undo_retrans accounting in tcp_sacktag_one()

On Mon, Sep 13, 2021 at 12:11 PM Yuchung Cheng <ycheng@...gle.com> wrote:
>
> On Mon, Sep 13, 2021 at 8:49 AM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > On Mon, Sep 13, 2021 at 3:51 AM zhenggy <zhenggy@...natelecom.cn> wrote:
> > >
> > > Commit 10d3be569243 ("tcp-tso: do not split TSO packets at retransmit
> > > time") may directly retrans a multiple segments TSO/GSO packet without
> > > split, Since this commit, we can no longer assume that a retransmitted
> > > packet is a single segment.
> > >
> > > This patch fixes the tp->undo_retrans accounting in tcp_sacktag_one()
> > > that use the actual segments(pcount) of the retransmitted packet.
> > >
> > > Before that commit (10d3be569243), the assumption underlying the
> > > tp->undo_retrans-- seems correct.
> > >
> > > Fixes: 10d3be569243 ("tcp-tso: do not split TSO packets at retransmit time")
> > >
> >
> > nit: We normally do not add an empty line between Fixes: tag and others.
> >
> > Reviewed-by: Eric Dumazet <edumazet@...gle.com>
> Acked-by: Yuchung Cheng <ycheng@...gle.com>
>
> This is a nice fix that would increase the effectiveness of TCP undo
> in high-speed networks.

Yes, thanks for the fix!

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

neal