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

[Vincent Guittot]

On 25 March 2015 at 18:33, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Tue, Mar 24, 2015 at 11:00:57AM +0100, Vincent Guittot wrote:
>> On 23 March 2015 at 14:19, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>> > On Fri, Feb 27, 2015 at 04:54:07PM +0100, Vincent Guittot wrote:
>> >
>> >> +     unsigned long scale_freq = arch_scale_freq_capacity(NULL, cpu);
>> >
>> >> +                     sa->running_avg_sum += delta_w * scale_freq
>> >> +                             >> SCHED_CAPACITY_SHIFT;
>> >
>> > so the only thing that could be improved is somehow making this
>> > multiplication go away when the arch doesn't implement the function.
>> >
>> > But I'm not sure how to do that without #ifdef.
>> >
>> > Maybe a little something like so then... that should make the compiler
>> > get rid of those multiplications unless the arch needs them.
>>
>> yes, it removes useless multiplication when not used by an arch.
>> It also adds a constraint on the arch side which have to define
>> arch_scale_freq_capacity like below:
>>
>> #define arch_scale_freq_capacity xxx_arch_scale_freq_capacity
>> with xxx_arch_scale_freq_capacity an architecture specific function
>
> Yeah, but it not being weak should make that a compile time warn/fail,
> which should be pretty easy to deal with.
>
>> If it sounds acceptable i can update the patch with your proposal ?
>
> I'll stick it to the end, I just wanted to float to patch to see if
> people had better solutions.

ok. all other methods that i have tried, was removing the optimization
when default arch_scale_freq_capacity was used
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