netdev - Re: [PATCH net] tcp: Do not underestimate rwnd

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Date:   Wed, 5 Dec 2018 14:33:22 -0800
From:   Yuchung Cheng <ycheng@...gle.com>
To:     Soheil Hassas Yeganeh <soheil@...gle.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Neal Cardwell <ncardwell@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net] tcp: Do not underestimate rwnd_limited

On Wed, Dec 5, 2018 at 2:28 PM Soheil Hassas Yeganeh <soheil@...gle.com> wrote:
>
> On Wed, Dec 5, 2018 at 5:24 PM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > If available rwnd is too small, tcp_tso_should_defer()
> > can decide it is worth waiting before splitting a TSO packet.
> >
> > This really means we are rwnd limited.
> >
> > Fixes: 5615f88614a4 ("tcp: instrument how long TCP is limited by receive window")
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>
> Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>
Reviewed-by: Yuchung Cheng <ycheng@...gle.com>
>
> Excellent catch! Thank you for the fix, Eric!
>
> > ---
> >  net/ipv4/tcp_output.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> > index 68b5326f73212ffe7111dd0f91e0a1246fb0ae25..3186902347584090256467d8679320666aa0257e 100644
> > --- a/net/ipv4/tcp_output.c
> > +++ b/net/ipv4/tcp_output.c
> > @@ -2356,8 +2356,11 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
> >                 } else {
> >                         if (!push_one &&
> >                             tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
> > -                                                max_segs))
> > +                                                max_segs)) {
> > +                               if (!is_cwnd_limited)
> > +                                       is_rwnd_limited = true;
> >                                 break;
> > +                       }
> >                 }
> >
> >                 limit = mss_now;
> > --
> > 2.20.0.rc2.403.gdbc3b29805-goog
> >