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

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On 13 April 2017 at 18:13, Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, Apr 13, 2017 at 05:16:20PM +0200, Vincent Guittot wrote:
>> On 13 April 2017 at 15:39, Peter Zijlstra <peterz@infradead.org> wrote:
>
>> > OK, so the reason util_avg varies is because we compute it wrong. And I
>> > think we can easily fix that once we pull out all the factors (which
>> > would mean your patch and the pulling out of weight patch which still
>> > needs to be finished).
>>
>> That would be great to remove this unwanted variation.
>
> So the problem with the _avg stuff is that we include the d3 segment,
> that is the unfinished current window. Since we only re-compute the _avg
> whenever we roll over, the intent already seems to be to only compute it
> on completed windows.

yes make sense

>
> But because 'complicated/expensive', its hard to not include d3 and thus
> we get the wobble.
>
> Once we compute pure running/runnable sums, without extra contrib
> factors, we can simply subtract our d3 term from sum when doing the
> division and change the divider to LOAD_AVG_MAX*y, getting the stable
> _avg over all completed windows.

I'm going to make it a try to check that it removes the variation i'm seeing

>
> (you could do the same with factors, but then we get to do a bunch of
> extra multiplications which aren't free).
>
>> >
>> > But you're comparing against util_sum here, that behaves slightly
>> > different. I think you want 'util_sum >= 1024 * (LOAD_AVG_MAX - 1024)'
>> > instead.
>>
>> yes, the variation happens on the util_sum
>
> Well, for util_sum its simple to ignore the current window, which is
> what the suggested equation does (note that LOAD_AVG_MAX*y ==
> LOAD_AVG_MAX-1024).

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Re: [PATCH v2] sched/fair: update scale invariance of PELT Peter Zijlstra <peterz@infradead.org> - 2017-04-10 19:40 +0200
  Re: [PATCH v2] sched/fair: update scale invariance of PELT Vincent Guittot <vincent.guittot@linaro.org> - 2017-04-11 10:00 +0200
    Re: [PATCH v2] sched/fair: update scale invariance of PELT Peter Zijlstra <peterz@infradead.org> - 2017-04-11 11:00 +0200
      Re: [PATCH v2] sched/fair: update scale invariance of PELT Vincent Guittot <vincent.guittot@linaro.org> - 2017-04-11 11:50 +0200
        Re: [PATCH v2] sched/fair: update scale invariance of PELT Peter Zijlstra <peterz@infradead.org> - 2017-04-11 12:50 +0200
          Re: [PATCH v2] sched/fair: update scale invariance of PELT Peter Zijlstra <peterz@infradead.org> - 2017-04-11 13:00 +0200
            Re: [PATCH v2] sched/fair: update scale invariance of PELT Vincent Guittot <vincent.guittot@linaro.org> - 2017-04-11 15:10 +0200
              Re: [PATCH v2] sched/fair: update scale invariance of PELT Peter Zijlstra <peterz@infradead.org> - 2017-04-12 13:30 +0200
                Re: [PATCH v2] sched/fair: update scale invariance of PELT Vincent Guittot <vincent.guittot@linaro.org> - 2017-04-12 17:00 +0200
                Re: [PATCH v2] sched/fair: update scale invariance of PELT Peter Zijlstra <peterz@infradead.org> - 2017-04-12 17:50 +0200
                Re: [PATCH v2] sched/fair: update scale invariance of PELT Vincent Guittot <vincent.guittot@linaro.org> - 2017-04-13 11:50 +0200
                Re: [PATCH v2] sched/fair: update scale invariance of PELT Peter Zijlstra <peterz@infradead.org> - 2017-04-13 15:40 +0200
                Re: [PATCH v2] sched/fair: update scale invariance of PELT Vincent Guittot <vincent.guittot@linaro.org> - 2017-04-13 17:00 +0200
                Re: [PATCH v2] sched/fair: update scale invariance of PELT Peter Zijlstra <peterz@infradead.org> - 2017-04-13 20:10 +0200
                Re: [PATCH v2] sched/fair: update scale invariance of PELT Vincent Guittot <vincent.guittot@linaro.org> - 2017-04-14 10:50 +0200
          Re: [PATCH v2] sched/fair: update scale invariance of PELT Vincent Guittot <vincent.guittot@linaro.org> - 2017-04-11 14:10 +0200
    Re: [PATCH v2] sched/fair: update scale invariance of PELT Peter Zijlstra <peterz@infradead.org> - 2017-04-11 11:20 +0200
      Re: [PATCH v2] sched/fair: update scale invariance of PELT Vincent Guittot <vincent.guittot@linaro.org> - 2017-04-11 11:50 +0200
    Re: [PATCH v2] sched/fair: update scale invariance of PELT Peter Zijlstra <peterz@infradead.org> - 2017-04-13 15:40 +0200
      Re: [PATCH v2] sched/fair: update scale invariance of PELT Vincent Guittot <vincent.guittot@linaro.org> - 2017-04-13 17:20 +0200
        Re: [PATCH v2] sched/fair: update scale invariance of PELT Peter Zijlstra <peterz@infradead.org> - 2017-04-13 18:20 +0200
          Re: [PATCH v2] sched/fair: update scale invariance of PELT Vincent Guittot <vincent.guittot@linaro.org> - 2017-04-14 11:00 +0200
            Re: [PATCH v2] sched/fair: update scale invariance of PELT Vincent Guittot <vincent.guittot@linaro.org> - 2017-04-19 18:40 +0200

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