Date: Wed, 26 Oct 2022 13:59:32 +0100 From: Tom Jones <thj@freebsd.org> To: tuexen@freebsd.org Cc: Hans Petter Selasky <hps@selasky.org>, Zhenlei Huang <zlei.huang@gmail.com>, freebsd-net@freebsd.org Subject: Re: Too aggressive TCP ACKs Message-ID: <Y1kvNBMedJtrs6yo@spacemonster> In-Reply-To: <4E92E238-798B-4293-B0D2-81E3FCB92E34@freebsd.org> 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> <1ed66217-5463-fd4d-7e7a-58d9981bc44c@selasky.org> <Y1j2ZzHaFt/YA5Et@spacemonster> <4E92E238-798B-4293-B0D2-81E3FCB92E34@freebsd.org>
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On Wed, Oct 26, 2022 at 02:55:21PM +0200, tuexen@freebsd.org wrote: > > On 26. Oct 2022, at 10:57, Tom Jones <thj@freebsd.org> wrote: > > > > On Sat, Oct 22, 2022 at 12:14:25PM +0200, Hans Petter Selasky wrote: > >> 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. > >> > > > > Changing the ACK ratio seems to be okay in most cases, a paper I wrote > > about this was published this week: > > > > https://onlinelibrary.wiley.com/doi/10.1002/sat.1466 > > > > It focuses on QUIC, but congestion control dynamics don't change with > > the protocol. You should be able to read there, but if not I'm happy to > > send anyone a pdf. > Is QUIC using an L=2 for ABC? I think that is the rfc recommendation, actual deployed reality is more scattershot. - Tom
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