Re: [iccrg] [bbr-dev] cwnd 4 in BBRv2?
Neal Cardwell <ncardwell@google.com> Fri, 29 March 2019 00:03 UTC
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From: Neal Cardwell <ncardwell@google.com>
Date: Fri, 29 Mar 2019 01:03:05 +0100
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To: Dave Taht <dave.taht@gmail.com>
Cc: ECN-Sane <ecn-sane@lists.bufferbloat.net>, BBR Development <bbr-dev@googlegroups.com>, iccrg IRTF list <iccrg@irtf.org>
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Subject: Re: [iccrg] [bbr-dev] cwnd 4 in BBRv2?
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On Thu, Mar 28, 2019 at 6:10 PM Dave Taht <dave.taht@gmail.com> wrote: > > I just finished watching the sessions in ietf iccrg... > > and although I have many questions about BBRv2, I am curious if the > cwnd in it is capped to a minimum of 4, not 2, still? BBRv1 is... > > https://github.com/torvalds/linux/blob/master/net/ipv4/tcp_bbr.c#L385 So far that part of the algorithm has not changed in BBRv2. So, except for certain corner cases in loss recovery (e.g. cwnd=1 on RTO), the min cwnd is generally 4. But keep in mind that BBR generally tries to be pacing-limited, rather than cwnd-limited. And below a cwnd of 4 delayed ACKs can inhibit pipelining, causing stop-and-wait-type problems that significantly hurt throughput. best, neal
- [iccrg] cwnd 4 in BBRv2? Dave Taht
- Re: [iccrg] [bbr-dev] cwnd 4 in BBRv2? Neal Cardwell