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Date: Fri, 14 Jan 2022 14:20:50 -0800 From: Ivan Babrou <ivan@...udflare.com> To: Dave Taht <dave.taht@...il.com> Cc: bpf <bpf@...r.kernel.org>, Linux Kernel Network Developers <netdev@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, kernel-team <kernel-team@...udflare.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <kafai@...com>, Eric Dumazet <edumazet@...gle.com> Subject: Re: [PATCH bpf-next] tcp: bpf: Add TCP_BPF_RCV_SSTHRESH for bpf_setsockopt On Thu, Jan 13, 2022 at 9:44 PM Dave Taht <dave.taht@...il.com> wrote: > Yes, but with the caveats below. I'm fine with you just saying round trips, > and making this api possible. > > It would comfort me further if you could provide an actual scenario. The actual scenario is getting a response as quickly as possible on a fresh connection across long distances (200ms+ RTT). If an RPC response doesn't fit into the initial 64k of rcv_ssthresh, we end up requiring more roundrips to receive the response. Some customers are very picky about the latency they measure and cutting the extra roundtrips made a very visible difference in the tests. > See also: > > https://datatracker.ietf.org/doc/html/rfc6928 > > which predates packet pacing (are you using sch_fq?) We are using fq and bbr. > > Congestion window is a learned property, not a static number. You > > won't get a large initcwnd towards a poor connection. > > initcwnd is set globally or on a per route basis. With TCP_BPF_IW the world is your oyster.
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