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Date:      Sat, 22 Oct 2022 12:14:25 +0200
From:      Hans Petter Selasky <hps@selasky.org>
To:        Zhenlei Huang <zlei.huang@gmail.com>, Michael Tuexen <michael.tuexen@lurchi.franken.de>
Cc:        freebsd-net@freebsd.org
Subject:   Re: Too aggressive TCP ACKs
Message-ID:  <1ed66217-5463-fd4d-7e7a-58d9981bc44c@selasky.org>
In-Reply-To: <330A9146-F7CC-4CAB-9003-2F90B872AC3E@gmail.com>
References:  <75D35F36-7759-4168-ADBA-C2414F5B53BC@gmail.com> <712641B3-5196-40CC-9B64-04637F16F649@lurchi.franken.de> <62A0DD30-B3ED-48BE-9C01-146487599092@gmail.com> <0FED34A9-D093-442A-83B7-08C06D11F8B5@lurchi.franken.de> <330A9146-F7CC-4CAB-9003-2F90B872AC3E@gmail.com>

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Hi,

Some thoughts about this topic.

Delaying ACKs means loss of performance when using Gigabit TCP 
connections in data centers. There it is important to ACK the data as 
quick as possible, to avoid running out of TCP window space. Thinking 
about TCP connections at 30 GBit/s and above!

I think the implementation should be exactly like it is.

There is a software LRO in FreeBSD to coalesce the ACKs before they hit 
the network stack, so there are no real problems there.

--HPS





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