linux-kernel - Re: [PATCH v5 1/3] sched/fair: Introduce the burstable CFS controller

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Message-ID: <YKzVu2cOYRN9TZD3@hirez.programming.kicks-ass.net>
Date:   Tue, 25 May 2021 12:47:23 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     changhuaixin <changhuaixin@...ux.alibaba.com>
Cc:     Benjamin Segall <bsegall@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        dtcccc@...ux.alibaba.com, Juri Lelli <juri.lelli@...hat.com>,
        khlebnikov@...dex-team.ru,
        open list <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...e.de>, Ingo Molnar <mingo@...hat.com>,
        Odin Ugedal <odin@...d.al>, Odin Ugedal <odin@...dal.com>,
        pauld@...head.com, Paul Turner <pjt@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Shanpei Chen <shanpeic@...ux.alibaba.com>,
        Tejun Heo <tj@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        xiyou.wangcong@...il.com
Subject: Re: [PATCH v5 1/3] sched/fair: Introduce the burstable CFS controller

On Mon, May 24, 2021 at 08:42:03PM +0800, changhuaixin wrote:

> >> static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
> >> @@ -4651,6 +4666,9 @@ static int __assign_cfs_rq_runtime(struct cfs_bandwidth *cfs_b,
> >> 	if (cfs_b->quota == RUNTIME_INF)
> >> 		amount = min_amount;
> >> 	else {
> >> +		if (!cfs_b->period_active)
> >> +			__refill_cfs_bandwidth_runtime(cfs_b);
> > 
> > Why this call?
> 
> As the cfs bandwidth timer stops on idle with runtime unfilled, refill runtime when it restarts to make
> use of the underrun when period timer stops. Another way to do this might be:
> 
>         throttled = !list_empty(&cfs_b->throttled_cfs_rq);
>         cfs_b->nr_periods += overrun;
> 
> +       __refill_cfs_bandwidth_runtime(cfs_b);
> +
>         /*
>          * idle depends on !throttled (for the case of a large deficit), and if
>          * we're going inactive then everything else can be deferred
>          */
>         if (cfs_b->idle && !throttled)
>                 goto out_deactivate;
> 
> -       __refill_cfs_bandwidth_runtime(cfs_b);
> -
>         if (!throttled) {
> 

Ben, do you have a preference?