Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl

[Yuchung Cheng]

On Tue, Oct 10, 2023 at 3:14 PM Stephen Hemminger
<stephen@xxxxxxxxxxxxxxxxxx> wrote:
>
> On Tue, 10 Oct 2023 12:23:30 -0700
> Haiyang Zhang <haiyangz@xxxxxxxxxxxxx> 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 quick
> > 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@xxxxxxxxxxxxx>
>
> If this an application specific optimization, it should be in a socket option
> 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