linux-kernel - Re: [PATCH 2/2] sched/fair: Advance global expiration when period timer is restarted

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Message-ID: <CAM_iQpV-9_Q_xdNAobSq1bZXPm0kALAq1+Jc3BFpVAaQ2E_czQ@mail.gmail.com>
Date:   Mon, 18 Jun 2018 21:36:49 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Xunlei Pang <xlpang@...ux.alibaba.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Ben Segall <bsegall@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] sched/fair: Advance global expiration when period
 timer is restarted

On Mon, Jun 18, 2018 at 2:16 AM, Xunlei Pang <xlpang@...ux.alibaba.com> wrote:
> I noticed the group frequently got throttled even it consumed
> low cpu usage, this caused some jitters on the response time
> to some of our business containers enabling cpu quota.
>
> It's very easy to reproduce:
> mkdir /sys/fs/cgroup/cpu/test
> cd /sys/fs/cgroup/cpu/test
> echo 100000 > cpu.cfs_quota_us
> echo $$ > tasks
> then repeat:
> cat cpu.stat |grep nr_throttled  // nr_throttled will increase
>
> After some analysis, we found that cfs_rq::runtime_remaining will
> be cleared by expire_cfs_rq_runtime() due to two equal but stale
> "cfs_{b|q}->runtime_expires" after period timer is re-armed.
>
> The global expiration should be advanced accordingly when the
> bandwidth period timer is restarted.
>

I observed the same problem and already sent some patches:

https://lkml.org/lkml/2018/5/22/37
https://lkml.org/lkml/2018/5/22/38
https://lkml.org/lkml/2018/5/22/35