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Message-ID: <CADVnQykHjVfqP75pxOKMAx2q+_n-e1yk8j_xdNKjudG3K6pC5w@mail.gmail.com> Date: Tue, 17 Oct 2023 11:25:54 -0400 From: Neal Cardwell <ncardwell@...gle.com> To: Eric Dumazet <edumazet@...gle.com> Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, eric.dumazet@...il.com, Stefan Wahren <wahrenst@....net> Subject: Re: [PATCH net] tcp: tsq: relax tcp_small_queue_check() when rtx queue contains a single skb On Tue, Oct 17, 2023 at 8:45 AM Eric Dumazet <edumazet@...gle.com> wrote: > > In commit 75eefc6c59fd ("tcp: tsq: add a shortcut in tcp_small_queue_check()") > we allowed to send an skb regardless of TSQ limits being hit if rtx queue > was empty or had a single skb, in order to better fill the pipe > when/if TX completions were slow. > > Then later, commit 75c119afe14f ("tcp: implement rb-tree based > retransmit queue") accidentally removed the special case for > one skb in rtx queue. > > Stefan Wahren reported a regression in single TCP flow throughput > using a 100Mbit fec link, starting from commit 65466904b015 ("tcp: adjust > TSO packet sizes based on min_rtt"). This last commit only made the > regression more visible, because it locked the TCP flow on a particular > behavior where TSQ prevented two skbs being pushed downstream, > adding silences on the wire between each TSO packet. > > Many thanks to Stefan for his invaluable help ! > > Fixes: 75c119afe14f ("tcp: implement rb-tree based retransmit queue") > Link: https://lore.kernel.org/netdev/7f31ddc8-9971-495e-a1f6-819df542e0af@gmx.net/ > Reported-by: Stefan Wahren <wahrenst@....net> > Tested-by: Stefan Wahren <wahrenst@....net> > Signed-off-by: Eric Dumazet <edumazet@...gle.com> > Cc: Neal Cardwell <ncardwell@...gle.com> > --- Acked-by: Neal Cardwell <ncardwell@...gle.com> Thank you to Eric for the nice find and fix, and thank you to Stefan for the bug report and all the useful testing and data! neal
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