linux-kernel - Re: [RFC 1/4] sched: extend the usage of cpu_power

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Date:	Tue, 1 Apr 2014 13:20:17 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	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>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Mike Galbraith <efault@....de>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>
Subject: Re: [RFC 1/4] sched: extend the usage of cpu_power_orig

On 1 April 2014 12:39, Preeti U Murthy <preeti@...ux.vnet.ibm.com> wrote:
> Hi Vincent,
>
> On 03/28/2014 06:52 PM, Vincent Guittot wrote:
>> cpu_power_orig is only changed for SMT system 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.
>
> There is no parameter 'cpu_power_orig' till your fourth patch right?
> Why is this term being used in this patch?

It looks like that i have mixed power_orig and cpu_power_orig in my
commit messages

>
> Besides, both parameters power and power_orig are changed for SMT
> systems to reflect the lower capacity of the CPUs.Why is there a mention
> of only power_orig?

Only SMT system is able to change power_orig from default value
whereas all systems can already change power field with
arch_scale_freq_power function. The goal of this patch is to change
the function name that is used to set power_orig value to a more
generic one and to extend the possibility of setting power_orig for
any kind of system. The behavior of the power field is not changed
with this patchset.

>
> IMO, the subject of the patch is not clearly reflecting the main
> intention of the patch. There is nothing done to change the way
> cpu_power is used; rather you are changing the way the cpu_power is
> being set to be flexible, thus allowing for the right power value to be
> set on heterogeneous systems.
>
> 'Allow archs to set the cpu_power instead of falling to default value'
> or something similar would be more appropriate. What do you think?

I can change with : "Allow all archs to set the power_orig"

Thanks

>
> Regards
> Preeti U Murthy
>>
>> Create a more generic function arch_scale_cpu_power that can be also used by
>> non SMT platform to set cpu_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 cpu_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 7e9bd0b..ed42061 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -5559,6 +5559,20 @@ unsigned long __weak arch_scale_smt_power(struct sched_domain *sd, int cpu)
>>       return default_scale_smt_power(sd, cpu);
>>  }
>>
>> +unsigned long __weak arch_scale_cpu_power(struct sched_domain *sd, int cpu)
>> +{
>> +     unsigned long weight = sd->span_weight;
>> +
>> +     if ((sd->flags & SD_SHARE_CPUPOWER) && weight > 1) {
>> +             if (sched_feat(ARCH_POWER))
>> +                     return arch_scale_smt_power(sd, cpu);
>> +             else
>> +                     return default_scale_smt_power(sd, cpu);
>> +     }
>> +
>> +     return SCHED_POWER_SCALE;
>> +}
>> +
>>  static unsigned long scale_rt_power(int cpu)
>>  {
>>       struct rq *rq = cpu_rq(cpu);
>> @@ -5590,18 +5604,12 @@ static unsigned long scale_rt_power(int cpu)
>>
>>  static void update_cpu_power(struct sched_domain *sd, int cpu)
>>  {
>> -     unsigned long weight = sd->span_weight;
>>       unsigned long power = SCHED_POWER_SCALE;
>>       struct sched_group *sdg = sd->groups;
>>
>> -     if ((sd->flags & SD_SHARE_CPUPOWER) && weight > 1) {
>> -             if (sched_feat(ARCH_POWER))
>> -                     power *= arch_scale_smt_power(sd, cpu);
>> -             else
>> -                     power *= default_scale_smt_power(sd, cpu);
>> +     power *= arch_scale_cpu_power(sd, cpu);
>>
>> -             power >>= SCHED_POWER_SHIFT;
>> -     }
>> +     power >>= SCHED_POWER_SHIFT;
>>
>>       sdg->sgp->power_orig = power;
>>
>
--
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