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From:   Benjamin Segall <bsegall@google.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     changhuaixin <changhuaixin@linux.alibaba.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        dtcccc@linux.alibaba.com, Juri Lelli <juri.lelli@redhat.com>,
        khlebnikov@yandex-team.ru,
        open list <linux-kernel@vger.kernel.org>,
        Mel Gorman <mgorman@suse.de>, Ingo Molnar <mingo@redhat.com>,
        Odin Ugedal <odin@uged.al>, Odin Ugedal <odin@ugedal.com>,
        pauld@redhead.com, Paul Turner <pjt@google.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Shanpei Chen <shanpeic@linux.alibaba.com>,
        Tejun Heo <tj@kernel.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        xiyou.wangcong@gmail.com
Subject: Re: [PATCH v5 1/3] sched/fair: Introduce the burstable CFS controller
References: <20210520123419.8039-1-changhuaixin@linux.alibaba.com>
        <20210520123419.8039-2-changhuaixin@linux.alibaba.com>
        <YKe89Uda+uJdx4X0@hirez.programming.kicks-ass.net>
        <C759D4F2-FA5F-4EB2-8441-C9ECD79AFD55@linux.alibaba.com>
        <YKzVu2cOYRN9TZD3@hirez.programming.kicks-ass.net>
Date:   Tue, 25 May 2021 14:25:33 -0700
In-Reply-To: <YKzVu2cOYRN9TZD3@hirez.programming.kicks-ass.net> (Peter
        Zijlstra's message of "Tue, 25 May 2021 12:47:23 +0200")
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Peter Zijlstra <peterz@infradead.org> writes:

> 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?


I think I prefer the latter, possibly with a
/* Refill extra burst quota even if cfs_b->idle */