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

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Date:   Tue, 19 Jun 2018 13:46:31 +0800
From:   Xunlei Pang <xlpang@...ux.alibaba.com>
To:     Cong Wang <xiyou.wangcong@...il.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 6/19/18 12:36 PM, Cong Wang wrote:
> 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
> 

Looks they are related to large slice setting and unused slack
under large number of cpus, the issue I described is a little
different.