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

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Date:   Tue, 30 Aug 2022 11:19:24 +0800
From:   "zhaowenhui (A)" <zhaowenhui8@...wei.com>
To:     <mingo@...hat.com>, <peterz@...radead.org>,
        <juri.lelli@...hat.com>, <vincent.guittot@...aro.org>,
        <dietmar.eggemann@....com>, <rostedt@...dmis.org>,
        <bsegall@...gle.com>, <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>
CC:     <zhaogongyi@...wei.com>
Subject: Re: [PATCH] sched/fair: limit burst to zero when cfs bandwidth is
 toggled off



在 2022/8/9 20:03, Zhao Wenhui 写道:
> 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>
> ---
>   kernel/sched/core.c | 10 +++++++++-
>   1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index ee28253c9ac0..4c1fc01d8c68 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -10584,6 +10584,12 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota,
>   				     burst + quota > max_cfs_runtime))
>   		return -EINVAL;
>   
> +	/*
> +	 * Ensure burst equals to zero when quota is -1.
> +	 */
> +	if (quota == RUNTIME_INF && burst)
> +		return -EINVAL;
> +
>   	/*
>   	 * Prevent race between setting of cfs_rq->runtime_enabled and
>   	 * unthrottle_offline_cfs_rqs().
> @@ -10643,8 +10649,10 @@ static int tg_set_cfs_quota(struct task_group *tg, long cfs_quota_us)
>   
>   	period = ktime_to_ns(tg->cfs_bandwidth.period);
>   	burst = tg->cfs_bandwidth.burst;
> -	if (cfs_quota_us < 0)
> +	if (cfs_quota_us < 0) {
>   		quota = RUNTIME_INF;
> +		burst = 0;
> +	}
>   	else if ((u64)cfs_quota_us <= U64_MAX / NSEC_PER_USEC)
>   		quota = (u64)cfs_quota_us * NSEC_PER_USEC;
>   	else

Gentle ping.

Thanks,
Zhao Wenhui