linux-kernel - Re: [PATCH 2/4] sched/fair: Move avg_scan_cost calculations under SIS

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Message-ID: <14963d1e-02ea-c298-d6b4-2db637913ee3@linux.intel.com>
Date:   Wed, 9 Dec 2020 19:07:11 +0800
From:   "Li, Aubrey" <aubrey.li@...ux.intel.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Peter Ziljstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Linux-ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/4] sched/fair: Move avg_scan_cost calculations under
 SIS_PROP

On 2020/12/9 17:05, Mel Gorman wrote:
> On Wed, Dec 09, 2020 at 01:28:11PM +0800, Li, Aubrey wrote:
>>>>                         nr = div_u64(span_avg, avg_cost);
>>>>                 else
>>>>                         nr = 4;
>>>> -       }
>>>> -
>>>> -       time = cpu_clock(this);
>>>>
>>>> -       cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
>>>> +               time = cpu_clock(this);
>>>> +       }
>>>>
>>>>         for_each_cpu_wrap(cpu, cpus, target) {
>>>>                 if (!--nr)
>>
>> nr is the key of this throttling mechanism, need to be placed under sched_feat(SIS_PROP) as well.
>>
> 
> It isn't necessary as nr in initialised to INT_MAX if !SIS_PROP.
>If !SIS_PROP, nr need to -1 then tested in the loop, instead of testing directly.
But with SIS_PROP, need adding a test in the loop.
Since SIS_PROP is default true, I think it's okay to keep the current way.

Thanks,
-Aubrey