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Date:   Tue, 10 Oct 2023 15:14:04 -0700
From:   Stephen Hemminger <stephen@networkplumber.org>
To:     Haiyang Zhang <haiyangz@microsoft.com>
Cc:     linux-hyperv@vger.kernel.org, netdev@vger.kernel.org,
        kys@microsoft.com, davem@davemloft.net, edumazet@google.com,
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        linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl
Message-ID: <20231010151404.3f7faa87@hermes.local>
In-Reply-To: <1696965810-8315-1-git-send-email-haiyangz@microsoft.com>
References: <1696965810-8315-1-git-send-email-haiyangz@microsoft.com>
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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 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@microsoft.com>

If this an application specific optimization, it should be in a socket option
rather than system wide via sysctl.