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

[Cong Wang]

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