linux-kernel - Re: [PATCH v2] sched/fair: update scale invariance of PELT

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Message-ID: <CAKfTPtA6aLm==_F9Zmo+4zHQks52nKyo8R7m1=zbYtWLQNeOvQ@mail.gmail.com>
Date:   Tue, 2 May 2017 15:38:12 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <Morten.Rasmussen@....com>,
        Yuyang Du <yuyang.du@...el.com>, Paul Turner <pjt@...gle.com>,
        Ben Segall <bsegall@...gle.com>
Subject: Re: [PATCH v2] sched/fair: update scale invariance of PELT

On 1 May 2017 at 11:00, Peter Zijlstra <peterz@...radead.org> wrote:
> On Sat, Apr 29, 2017 at 12:09:24AM +0200, Peter Zijlstra wrote:
>> On Mon, Apr 10, 2017 at 11:18:29AM +0200, Vincent Guittot wrote:
>> > +++ b/include/linux/sched.h
>> > @@ -313,6 +313,7 @@ struct load_weight {
>> >   */
>> >  struct sched_avg {
>> >     u64                             last_update_time;
>> > +   u64                             stolen_idle_time;
>> >     u64                             load_sum;
>> >     u32                             util_sum;
>> >     u32                             period_contrib;
>>
>> > +           if (sa->util_sum < (LOAD_AVG_MAX * 1000)) {
>> > +                   /*
>> > +                    * Add the idle time stolen by running at lower compute
>> > +                    * capacity
>> > +                    */
>> > +                   delta += sa->stolen_idle_time;
>> > +           }
>> > +           sa->stolen_idle_time = 0;
>>
>>
>> So I was wondering if stolen_idle_time really needs to be a u64. Afaict
>> we'll be at LOAD_AVG_MAX after LOAD_AVG_MAX_N periods, or LOAD_AVG_MAX_N
>> * LOAD_AVG_PERIOD time, which ends up being 11040.
>
> * 1024 or course, but still easily fits in u32.

Correct

>