From: Neal Cardwell <ncardwell@google.com>
To: Alexey Ivanov <savetherbtz@gmail.com>
Cc: bloat <bloat@lists.bufferbloat.net>
Subject: Re: [Bloat] Excessive throttling with fq
Date: Wed, 19 Feb 2020 08:52:16 -0500 [thread overview]
Message-ID: <CADVnQyn07y373=1Yxk7VVbVg6PWjau8ebriXq8TqOY3dyrknXw@mail.gmail.com> (raw)
In-Reply-To: <9dfa6edf-0b7a-981a-e980-1187e461f6eb@GMail.com>
On Wed, Feb 19, 2020 at 1:58 AM Alexey Ivanov <savetherbtz@gmail.com> wrote:
>
> FWIW, we recently noticed a similar issue with our CUBIC senders after
> we've enabled FQ on them (4.15 kernel.)
>
> Disabling train detection in hystart did fix the problem:
>
> # echo 2 > /sys/module/tcp_cubic/parameters/hystart_detect
>
> [1]
> https://github.com/torvalds/linux/blob/master/net/ipv4/tcp_cubic.c#L76-L77
Yes, Hystart was not designed to work with pacing, so when fq is used
Hystart ACK train detection needs to be disabled.
Eric Dumazet made some recent fixes (Linux v5.6) to make Hystart
dynamically adapt to the presence of pacing to avoid this issue:
473900a504e5 tcp_cubic: optimize hystart_update()
35821fc2b41c tcp_cubic: remove one conditional from hystart_update()
cff04e2da308 tcp_cubic: switch bictcp_clock() to usec resolution
42f3a8aaae66 tcp_cubic: tweak Hystart detection for short RTT flows
ede656e84658 tcp_cubic: make Hystart aware of pacing
f278b99ca6b2 tcp_cubic: refactor code to perform a divide only when needed
neal
prev parent reply other threads:[~2020-02-19 13:52 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-26 18:36 Hans-Kristian Bakke
2017-01-26 18:38 ` Hans-Kristian Bakke
2017-01-26 18:55 ` Hans-Kristian Bakke
2017-01-26 19:18 ` Eric Dumazet
2017-01-26 19:58 ` David Lang
2017-01-26 20:19 ` Hans-Kristian Bakke
2017-01-26 20:41 ` Eric Dumazet
2017-01-26 20:46 ` Hans-Kristian Bakke
2017-01-26 21:00 ` Eric Dumazet
[not found] ` <CAD_cGvFXR+Qb9_gnp=k4UttJZnrRRm4i19of7D4v8MK9EjeZ6Q@mail.gmail.com>
2017-01-26 21:07 ` Eric Dumazet
[not found] ` <CAD_cGvGuCU+R=ddTGTnLF3C8avmJ=UZyAYAkD0FQzd-v6fknPw@mail.gmail.com>
2017-01-26 21:33 ` Eric Dumazet
2017-01-26 20:54 ` Eric Dumazet
2017-01-26 20:57 ` Hans-Kristian Bakke
2020-02-19 6:58 ` Alexey Ivanov
2020-02-19 13:52 ` Neal Cardwell [this message]
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