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Message-ID: <988f6a55-739e-8eab-4755-302716ea908e@linux.alibaba.com>
Date:   Tue, 16 Aug 2022 13:24:13 +0800
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Subject: Re: [PATCH] sched/fair: limit burst to zero when cfs bandwidth is
 toggled off
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To:     Zhao Wenhui <zhaowenhui8@huawei.com>
Cc:     zhaogongyi@huawei.com, mingo@redhat.com, peterz@infradead.org,
        juri.lelli@redhat.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com,
        shanpeic@linux.alibaba.com, changhuaixin@linux.alibaba.com,
        tj@kernel.org, linux-kernel@vger.kernel.org
References: <20220809120320.19496-1-zhaowenhui8@huawei.com>
From:   Tianchen Ding <dtcccc@linux.alibaba.com>
In-Reply-To: <20220809120320.19496-1-zhaowenhui8@huawei.com>
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On 2022/8/9 20:03, Zhao Wenhui wrote:
> 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@huawei.com>
> Signed-off-by: Zhao Wenhui <zhaowenhui8@huawei.com>

Nice catch! Thanks for the fix.
Reviewed-by: Tianchen Ding <dtcccc@linux.alibaba.com>