linux-kernel - Re: [PATCH] sched/fair: limit burst to zero when cfs bandwidth is toggled off

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Message-ID: <xm26fshu4llh.fsf@google.com>
Date:   Wed, 17 Aug 2022 14:16:26 -0700
From:   Benjamin Segall <bsegall@...gle.com>
To:     Zhao Wenhui <zhaowenhui8@...wei.com>
Cc:     <mingo@...hat.com>, <peterz@...radead.org>,
        <juri.lelli@...hat.com>, <vincent.guittot@...aro.org>,
        <dietmar.eggemann@....com>, <rostedt@...dmis.org>,
        <mgorman@...e.de>, <bristot@...hat.com>, <vschneid@...hat.com>,
        <shanpeic@...ux.alibaba.com>, <changhuaixin@...ux.alibaba.com>,
        <tj@...nel.org>, <dtcccc@...ux.alibaba.com>,
        <linux-kernel@...r.kernel.org>, <zhaogongyi@...wei.com>
Subject: Re: [PATCH] sched/fair: limit burst to zero when cfs bandwidth is
 toggled off

Zhao Wenhui <zhaowenhui8@...wei.com> writes:

> When the quota value in CFS bandwidth is set to -1, that imples the
> cfs bandwidth is toggled off. So the burst feature is supposed to
> be disable as well.
>
> Currently, when quota is -1, burst will not be check, so that it can be
> set to almost arbitery value. Examples:
>         mkdir /sys/fs/cgroup/cpu/test
>         echo -1 > /sys/fs/cgroup/cpu/test/cpu.cfs_quota_us
>         echo 10000000000000000 > /sys/fs/cgroup/cpu/test/cpu.cfs_burst_us
>
> Moreover, after the burst modified by this way, quota can't be set
> to any value:
>         echo 100000 > cpu.cfs_quota_us
>         -bash: echo: write error: Invalid argument
>
> This patch can ensure the burst value being zero and unalterable,
> when quota is set to -1.
>
> Fixes: f4183717b370 ("sched/fair: Introduce the burstable CFS controller")
> Reported-by: Zhao Gongyi <zhaogongyi@...wei.com>
> Signed-off-by: Zhao Wenhui <zhaowenhui8@...wei.com>

Indeed, good catch.
Reviewed-by: Ben Segall <bsegall@...gle.com>