Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Benjamin Segall <bsegall@google.com>
To:     Zhao Wenhui <zhaowenhui8@huawei.com>
Cc:     <mingo@redhat.com>, <peterz@infradead.org>,
        <juri.lelli@redhat.com>, <vincent.guittot@linaro.org>,
        <dietmar.eggemann@arm.com>, <rostedt@goodmis.org>,
        <mgorman@suse.de>, <bristot@redhat.com>, <vschneid@redhat.com>,
        <shanpeic@linux.alibaba.com>, <changhuaixin@linux.alibaba.com>,
        <tj@kernel.org>, <dtcccc@linux.alibaba.com>,
        <linux-kernel@vger.kernel.org>, <zhaogongyi@huawei.com>
Subject: Re: [PATCH] sched/fair: limit burst to zero when cfs bandwidth is
 toggled off
References: <20220809120320.19496-1-zhaowenhui8@huawei.com>
Date:   Wed, 17 Aug 2022 14:16:26 -0700
In-Reply-To: <20220809120320.19496-1-zhaowenhui8@huawei.com> (Zhao Wenhui's
        message of "Tue, 9 Aug 2022 20:03:20 +0800")
Message-ID: <xm26fshu4llh.fsf@google.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.1 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Zhao Wenhui <zhaowenhui8@huawei.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@huawei.com>
> Signed-off-by: Zhao Wenhui <zhaowenhui8@huawei.com>

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