linux-kernel - RE: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl

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Message-ID: <PH7PR21MB3116FC142CAECCD5D981C530CACDA@PH7PR21MB3116.namprd21.prod.outlook.com>
Date:   Tue, 10 Oct 2023 22:59:49 +0000
From:   Haiyang Zhang <haiyangz@...rosoft.com>
To:     Yuchung Cheng <ycheng@...gle.com>,
        Stephen Hemminger <stephen@...workplumber.org>
CC:     "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "corbet@....net" <corbet@....net>,
        "dsahern@...nel.org" <dsahern@...nel.org>,
        "ncardwell@...gle.com" <ncardwell@...gle.com>,
        "kuniyu@...zon.com" <kuniyu@...zon.com>,
        "morleyd@...gle.com" <morleyd@...gle.com>,
        "mfreemon@...udflare.com" <mfreemon@...udflare.com>,
        "mubashirq@...gle.com" <mubashirq@...gle.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "weiwan@...gle.com" <weiwan@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl



> -----Original Message-----
> From: Yuchung Cheng <ycheng@...gle.com>
> Sent: Tuesday, October 10, 2023 6:27 PM
> To: Stephen Hemminger <stephen@...workplumber.org>
> Cc: Haiyang Zhang <haiyangz@...rosoft.com>; linux-hyperv@...r.kernel.org;
> netdev@...r.kernel.org; KY Srinivasan <kys@...rosoft.com>;
> davem@...emloft.net; edumazet@...gle.com; kuba@...nel.org;
> pabeni@...hat.com; corbet@....net; dsahern@...nel.org;
> ncardwell@...gle.com; kuniyu@...zon.com; morleyd@...gle.com;
> mfreemon@...udflare.com; mubashirq@...gle.com; linux-
> doc@...r.kernel.org; weiwan@...gle.com; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl
> 
> On Tue, Oct 10, 2023 at 3:14 PM Stephen Hemminger
> <stephen@...workplumber.org> wrote:
> >
> > On Tue, 10 Oct 2023 12:23:30 -0700
> > Haiyang Zhang <haiyangz@...rosoft.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 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@...rosoft.com>
> >
> > 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

Yes, the customer actually wants a global setting. But as suggested by Neal,
I changed it to be per-namespace to match other TCP tunables.

Thanks,
- Haiyang