linux-kernel - Re: [PATCH v3 04/12] sched: Allow all archs to set the power

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Date:	Thu, 10 Jul 2014 15:42:11 +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>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	LAK <linux-arm-kernel@...ts.infradead.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Mike Galbraith <efault@....de>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH v3 04/12] sched: Allow all archs to set the power_orig

On 9 July 2014 12:57, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, Jun 30, 2014 at 06:05:35PM +0200, Vincent Guittot wrote:
>> power_orig is only changed for system with a SMT sched_domain level in order to
>> reflect the lower capacity of CPUs. Heterogenous system also have to reflect an
>> original capacity that is different from the default value.
>>
>> Create a more generic function arch_scale_cpu_power that can be also used by
>> non SMT platform to set power_orig.
>>
>> The weak behavior of arch_scale_cpu_power is the previous SMT one in order to
>> keep backward compatibility in the use of power_orig.
>>
>> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
>> ---
>>  kernel/sched/fair.c | 24 ++++++++++++++++--------
>>  1 file changed, 16 insertions(+), 8 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 148b277..f0bba5f 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -5614,6 +5614,20 @@ unsigned long __weak arch_scale_smt_capacity(struct sched_domain *sd, int cpu)
>>       return default_scale_smt_capacity(sd, cpu);
>>  }
>>
>> +unsigned long __weak arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
>> +{
>> +     unsigned long weight = sd->span_weight;
>> +
>> +     if ((sd->flags & SD_SHARE_CPUCAPACITY) && weight > 1) {
>> +             if (sched_feat(ARCH_CAPACITY))
>> +                     return arch_scale_smt_capacity(sd, cpu);
>> +             else
>> +                     return default_scale_smt_capacity(sd, cpu);
>> +     }
>> +
>> +     return SCHED_CAPACITY_SCALE;
>> +}
>
> The only caller of arch_scale_smt_capacity is now an arch_ function
> itself; which makes it entirely redundant, no?
>
> Also, sched_feat() and default_scale_smt_capability() aren't available
> to arch implementations of this function and can thus not retain
> semantics.
>
> Seeing how we currently don't have any arch_scale_smt_capacity
> implementations other than the default we can easily replace it entirely
> with something like:
>
> unsigned long __weak arch_scale_cpu_capacity()
> {
>         if ((sd->flags & SD_SHARE_CPUCAPACITY) && (sd->span_weight > 1))
>                 return sd->smt_gain / sd->span_weight;
>
>         return SCHED_CAPACITY_SCALE;
> }
>
> Hmm?

That's fair. i'm going to clean up and remove unused function
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