linux-kernel - Re: [RFCv5 PATCH 40/46] sched/cpufreq_sched: compute freq_new based on capacity_orig

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Date:	Mon, 17 Aug 2015 13:19:59 +0100
From:	Juri Lelli <juri.lelli@....com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Michael Turquette <mturquette@...libre.com>
CC:	Morten Rasmussen <Morten.Rasmussen@....com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	"yuyang.du@...el.com" <yuyang.du@...el.com>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"sgurrappadi@...dia.com" <sgurrappadi@...dia.com>,
	"pang.xunlei@....com.cn" <pang.xunlei@....com.cn>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [RFCv5 PATCH 40/46] sched/cpufreq_sched: compute freq_new based
 on capacity_orig_of()

On 16/08/15 21:24, Peter Zijlstra wrote:
> On Sat, Aug 15, 2015 at 09:03:33PM -0700, Michael Turquette wrote:
>> Quoting Peter Zijlstra (2015-08-15 05:46:38)
>>> On Tue, Jul 07, 2015 at 07:24:23PM +0100, Morten Rasmussen wrote:
>>>> diff --git a/kernel/sched/cpufreq_sched.c b/kernel/sched/cpufreq_sched.c
>>>> index 2968f3a..7071528 100644
>>>> --- a/kernel/sched/cpufreq_sched.c
>>>> +++ b/kernel/sched/cpufreq_sched.c
>>>> @@ -184,7 +184,7 @@ void cpufreq_sched_set_cap(int cpu, unsigned long capacity)
>>>>               goto out;
>>>>  
>>>>       /* Convert the new maximum capacity request into a cpu frequency */
>>>> -     freq_new = capacity * policy->max >> SCHED_CAPACITY_SHIFT;
>>>> +     freq_new = (capacity * policy->max) / capacity_orig_of(cpu);
>>>>  
>>>>       /* No change in frequency? Bail and return current capacity. */
>>>>       if (freq_new == policy->cur)
>>>
>>> Can't we avoid exporting that lot by simply passing in the right values
>>> to begin with?
>>
>> By "right value" do you mean, "pass the frequency from cfs"?
> 
> Nah, just maybe: (capacity << SCHED_CAPACITY_SHIFT) / capacity_orig_of()
> such that you don't have to export that knowledge to this thing.
> 

Oh, right. I guess we can just go with something like:

 req_cap = get_cpu_usage(cpu) * capacity_margin / capacity_orig_of(cpu);

on fair.c side and switch back to

 freq_new = capacity * policy->max >> SCHED_CAPACITY_SHIFT;

on cpufreq_sched.c side. That saves us exporting capacity_orig_of().

Thanks,

- Juri

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