netdev - [QUERY] tcp: remove dubious FIN exception from tcp_cwnd

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Message-ID: <20250616072134.1649136-1-alok.a.tiwari@oracle.com>
Date: Mon, 16 Jun 2025 00:21:23 -0700
From: Alok Tiwari <alok.a.tiwari@...cle.com>
To: edumazet@...gle.com, ncardwell@...gle.com, kuniyu@...zon.com,
        davem@...emloft.net, dsahern@...nel.org, kuba@...nel.org,
        pabeni@...hat.com, horms@...nel.org
Cc: alok.a.tiwari@...cle.com, netdev@...r.kernel.org, darren.kenny@...cle.com
Subject: [QUERY] tcp: remove dubious FIN exception from tcp_cwnd_test()

Hi Eric,

Thanks for the cleanup and RFC conformance improvements.

However, we've observed a performance regression in our testing with 
Apachebench at higher concurrency levels. Specifically, throughput
and HTTP tail latency in workloads.
It seems the previous exception for FIN packets allowed graceful
tear-down even when CWND was full, which is now delayed or stalled.

We understand the motivation for the cleanup, but the change introduces
practical impact for real-world workloads relying on timely
FIN transmission.

Would you be open to discussing potential mitigations?( not sure like
selective FIN override, other approaches.)

Thanks again for your work on this.

Thanks,
Alok