Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 3 Jun 2019 11:49:05 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Liangyan <liangyan.peng@linux.alibaba.com>
Cc:     mingo@redhat.com, linux-kernel@vger.kernel.org,
        yun.wang@linux.alibaba.com, shanpeic@linux.alibaba.com,
        xlpang@linux.alibaba.com,
        "liangyan.ply" <liangyan.ply@linux.alibaba.com>,
        Ben Segall <bsegall@google.com>
Subject: Re: [PATCH] sched/fair: don't restart enqueued cfs quota slack timer
Message-ID: <20190603094905.GA3419@hirez.programming.kicks-ass.net>
References: <20190603044309.168065-1-liangyan.peng@linux.alibaba.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20190603044309.168065-1-liangyan.peng@linux.alibaba.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Jun 03, 2019 at 12:43:09PM +0800, Liangyan wrote:
> From: "liangyan.ply" <liangyan.ply@linux.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@linux.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
>