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

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Date:	Sat, 30 Aug 2014 22:37:40 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Vincent Guittot <vincent.guittot@...aro.org>, peterz@...radead.org,
	mingo@...nel.org, linux-kernel@...r.kernel.org,
	linux@....linux.org.uk, linux-arm-kernel@...ts.infradead.org
CC:	riel@...hat.com, Morten.Rasmussen@....com, efault@....de,
	nicolas.pitre@...aro.org, linaro-kernel@...ts.linaro.org,
	daniel.lezcano@...aro.org, dietmar.eggemann@....com
Subject: Re: [PATCH v5 04/12] sched: Allow all archs to set the capacity_orig

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'.

> 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?

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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