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

[Xunlei Pang]

On 6/19/18 12:36 PM, Cong Wang wrote:
> On Mon, Jun 18, 2018 at 2:16 AM, Xunlei Pang <xlpang@xxxxxxxxxxxxxxxxx> 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.