linux-kernel - Re: [PATCH] sched/fair: make CFS bandwidth slice per cpu group

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Message-ID: <CAM_iQpXPNKyCGzY3=9HaQYXCXx3hsU3a_6BsFM+6Hw--v5QZUQ@mail.gmail.com>
Date:   Mon, 30 Apr 2018 13:37:16 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, Paul Turner <pjt@...gle.com>,
        Mike Galbraith <efault@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] sched/fair: make CFS bandwidth slice per cpu group

On Mon, Apr 30, 2018 at 12:42 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, Apr 30, 2018 at 12:29:25PM -0700, Cong Wang wrote:
>> Currently, the sched_cfs_bandwidth_slice_us is a global setting which
>> affects all cgroups. Different groups may want different values based
>> on their own workload, one size doesn't fit all. The global pool filled
>> periodically is per cgroup too, they should have the right to distribute
>> their own quota to each local CPU with their own frequency.
>
> Why.. what happens? This doesn't really tell us anything.

We saw tasks in a container got throttled for many times even
when they don't apparently over-burn the CPU's. I tried to reduce
the sched_cfs_bandwidth_slice_us from the default 5ms to 1ms,
it solved the problem as no tasks got throttled after this change.
This is why I want to change it.

And I don't think 1ms will be good for all containers, so in order to
minimize the impact, I would like to keep the slice change within
each container. This is why I propose this patch rather just
`sysctl  -w`. Do you think otherwise?

BTW, people reported a similar (if not same) issue here before:
https://gist.github.com/bobrik/2030ff040fad360327a5fab7a09c4ff1

Thanks!