linux-kernel - Re: [PATCH] sched/fair: don't restart enqueued cfs quota slack timer

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Date:   Mon, 3 Jun 2019 11:49:05 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Liangyan <liangyan.peng@...ux.alibaba.com>
Cc:     mingo@...hat.com, linux-kernel@...r.kernel.org,
        yun.wang@...ux.alibaba.com, shanpeic@...ux.alibaba.com,
        xlpang@...ux.alibaba.com,
        "liangyan.ply" <liangyan.ply@...ux.alibaba.com>,
        Ben Segall <bsegall@...gle.com>
Subject: Re: [PATCH] sched/fair: don't restart enqueued cfs quota slack timer

On Mon, Jun 03, 2019 at 12:43:09PM +0800, Liangyan wrote:
> From: "liangyan.ply" <liangyan.ply@...ux.alibaba.com>
> 
> start_cfs_slack_bandwidth() will restart the quota slack timer,
> if it is called frequently, this timer will be restarted continuously
> and may have no chance to expire to unthrottle cfs tasks.
> This will cause that the throttled tasks can't be unthrottled in time
> although they have remaining quota.

This looks very similar to the patch from Ben here:

  https://lkml.kernel.org/r/xm26blzlyr9d.fsf@bsegall-linux.svl.corp.google.com

> 
> Signed-off-by: Liangyan <liangyan.peng@...ux.alibaba.com>
> ---
>  kernel/sched/fair.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d90a64620072..fdb03c752f97 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4411,9 +4411,11 @@ static void start_cfs_slack_bandwidth(struct cfs_bandwidth *cfs_b)
>  	if (runtime_refresh_within(cfs_b, min_left))
>  		return;
>  
> -	hrtimer_start(&cfs_b->slack_timer,
> +	if (!hrtimer_active(&cfs_b->slack_timer)) {
> +		hrtimer_start(&cfs_b->slack_timer,
>  			ns_to_ktime(cfs_bandwidth_slack_period),
>  			HRTIMER_MODE_REL);
> +	}
>  }
>  
>  /* we know any runtime found here is valid as update_curr() precedes return */
> -- 
> 2.14.4.44.g2045bb6
>