linux-kernel - Re: [PATCH v5 04/12] sched: Allow all archs to set the capacity

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Message-ID: <CAKfTPtCNPYOi9OY37nbG9o71n4i5mxxvrRow0SgL_9pVK1LpMA@mail.gmail.com>
Date:	Mon, 1 Sep 2014 10:05:09 +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>,
	Rik van Riel <riel@...hat.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 v5 04/12] sched: Allow all archs to set the capacity_orig

On 30 August 2014 19:07, Preeti U Murthy <preeti@...ux.vnet.ibm.com> wrote:
> Hi Vincent,
>
> On 08/26/2014 04:36 PM, Vincent Guittot wrote:
>> capacity_orig is only changed for system with a SMT sched_domain level in order
>
> I think I had asked this before, but why only capacity_orig? The
> capacity of a group is also being updated the same way. This patch fixes
> the capacity of a group to reflect the capacity of the heterogeneous
> CPUs in it, this capacity being both the full capacity of the group:
> capacity_orig and the capacity available for the fair tasks. So I feel
> in the subject as well as the changelog it would suffice to say 'capacity'.

IIRC, we discussed that point on a former version. The patch changes
only the behavior of capacity_orig but the behavior of capacity stays
unchanged as all archs can already set the capacity whereas the
capacity_orig was configurable only if the SD_SHARE_CPUCAPACITY was
set in the sched_domain. This is no more the case with this patch
which creates arch_scale_cpu_capacity for setting capacity_orig.

>
>> 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_capacity that can be also used by
>> non SMT platform to set capacity_orig.
>>
>> The weak behavior of arch_scale_cpu_capacity is the previous SMT one in order to
>> keep backward compatibility in the use of capacity_orig.
>>
>> arch_scale_smt_capacity and default_scale_smt_capacity have been removed as
>> they were not use elsewhere than in arch_scale_cpu_capacity.
>>
>> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
>> ---
>>  kernel/sched/fair.c | 25 ++++++-------------------
>>  1 file changed, 6 insertions(+), 19 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index b85e9f7..8176bda 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -5705,19 +5705,12 @@ unsigned long __weak arch_scale_freq_capacity(struct sched_domain *sd, int cpu)
>>       return default_scale_capacity(sd, cpu);
>>  }
>>
>> -static unsigned long default_scale_smt_capacity(struct sched_domain *sd, int cpu)
>> +unsigned long __weak arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
>>  {
>> -     unsigned long weight = sd->span_weight;
>> -     unsigned long smt_gain = sd->smt_gain;
>> +     if ((sd->flags & SD_SHARE_CPUCAPACITY) && (sd->span_weight > 1))
>> +             return sd->smt_gain / sd->span_weight;
>>
>> -     smt_gain /= weight;
>> -
>> -     return smt_gain;
>> -}
>> -
>> -unsigned long __weak arch_scale_smt_capacity(struct sched_domain *sd, int cpu)
>> -{
>> -     return default_scale_smt_capacity(sd, cpu);
>> +     return SCHED_CAPACITY_SCALE;
>>  }
>>
>>  static unsigned long scale_rt_capacity(int cpu)
>> @@ -5756,18 +5749,12 @@ static unsigned long scale_rt_capacity(int cpu)
>>
>>  static void update_cpu_capacity(struct sched_domain *sd, int cpu)
>>  {
>> -     unsigned long weight = sd->span_weight;
>>       unsigned long capacity = SCHED_CAPACITY_SCALE;
>>       struct sched_group *sdg = sd->groups;
>>
>> -     if ((sd->flags & SD_SHARE_CPUCAPACITY) && weight > 1) {
>> -             if (sched_feat(ARCH_CAPACITY))
>
> Aren't you missing this check above? I understand that it is not
> crucial, but that would also mean removing ARCH_CAPACITY sched_feat
> altogether, wouldn't it?

Peter has proposed to remove all those checks and to keep only the
default behavior because no arch uses arch_scale_smt_capacity.
Then, ARCH_CAPACITY is still used in update_cpu_capacity

Regards,
Vincent
>
> Regards
> Preeti U Murthy
>> -                     capacity *= arch_scale_smt_capacity(sd, cpu);
>> -             else
>> -                     capacity *= default_scale_smt_capacity(sd, cpu);
>> +     capacity *= arch_scale_cpu_capacity(sd, cpu);
>>
>> -             capacity >>= SCHED_CAPACITY_SHIFT;
>> -     }
>> +     capacity >>= SCHED_CAPACITY_SHIFT;
>>
>>       sdg->sgc->capacity_orig = capacity;
>>
>
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