Re: [PATCH v10 04/11] sched: Make sched entity usage tracking scale-invariant

[Vincent Guittot]

On 3 March 2015 at 13:51, Dietmar Eggemann <dietmar.eggemann@xxxxxxx> wrote:
> On 27/02/15 15:54, Vincent Guittot wrote:
>> From: Morten Rasmussen <morten.rasmussen@xxxxxxx>
>>
>> Apply frequency scale-invariance correction factor to usage tracking.
>> Each segment of the running_load_avg geometric series is now scaled by the
>
> The same comment I sent out on [PATCH v10 07/11]:
>
> The use of underscores in running_load_avg implies to me that this is a
> data member of struct sched_avg or something similar. But there is no
> running_load_avg in the current code. However, I can see that
> sched_avg::*running_avg_sum* (and therefore
> cfs_rq::*utilization_load_avg*) are frequency scale invariant.

I have resent the patch with typo correction

>
> -- Dietmar
>
>> current frequency so the utilization_avg_contrib of each entity will be
>> invariant with frequency scaling. As a result, utilization_load_avg which is
>> the sum of utilization_avg_contrib, becomes invariant too. So the usage level
>> that is returned by get_cpu_usage, stays relative to the max frequency as the
>> cpu_capacity which is is compared against.
>> Then, we want the keep the load tracking values in a 32bits type, which implies
>> that the max value of {runnable|running}_avg_sum must be lower than
>> 2^32/88761=48388 (88761 is the max weigth of a task). As LOAD_AVG_MAX = 47742,
>> arch_scale_freq_capacity must return a value less than
>> (48388/47742) << SCHED_CAPACITY_SHIFT = 1037 (SCHED_SCALE_CAPACITY = 1024).
>> So we define the range to [0..SCHED_SCALE_CAPACITY] in order to avoid overflow.
>
>
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