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From:   Yuchung Cheng <ycheng@google.com>
Date:   Tue, 10 Oct 2023 15:27:05 -0700
Message-ID: <CAK6E8=c576Gt=G9Wdk0gQi=2EiL_=6g1SA=mJ3HhzPCsLRk9tw@mail.gmail.com>
Subject: Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl
To:     Stephen Hemminger <stephen@networkplumber.org>
Cc:     Haiyang Zhang <haiyangz@microsoft.com>,
        linux-hyperv@vger.kernel.org, netdev@vger.kernel.org,
        kys@microsoft.com, davem@davemloft.net, edumazet@google.com,
        kuba@kernel.org, pabeni@redhat.com, corbet@lwn.net,
        dsahern@kernel.org, ncardwell@google.com, kuniyu@amazon.com,
        morleyd@google.com, mfreemon@cloudflare.com, mubashirq@google.com,
        linux-doc@vger.kernel.org, weiwan@google.com,
        linux-kernel@vger.kernel.org
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On Tue, Oct 10, 2023 at 3:14=E2=80=AFPM Stephen Hemminger
<stephen@networkplumber.org> wrote:
>
> On Tue, 10 Oct 2023 12:23:30 -0700
> Haiyang Zhang <haiyangz@microsoft.com> wrote:
>
> > TCP pingpong threshold is 1 by default. But some applications, like SQL=
 DB
> > may prefer a higher pingpong threshold to activate delayed acks in quic=
k
> > ack mode for better performance.
> >
> > The pingpong threshold and related code were changed to 3 in the year
> > 2019 in:
> >   commit 4a41f453bedf ("tcp: change pingpong threshold to 3")
> > And reverted to 1 in the year 2022 in:
> >   commit 4d8f24eeedc5 ("Revert "tcp: change pingpong threshold to 3"")
> >
> > There is no single value that fits all applications.
> > Add net.ipv4.tcp_pingpong_thresh sysctl tunable, so it can be tuned for
> > optimal performance based on the application needs.
> >
> > Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
>
> If this an application specific optimization, it should be in a socket op=
tion
> rather than system wide via sysctl.
Initially I had a similar comment but later decided a sysctl could
still be useful if
1) the entire host (e.g. virtual machine) is dedicated to that application
2) that application is difficult to change