linux-kernel - Re: [PATCH v2 05/11] ARM: topology: use new cpu

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Date:	Mon, 26 May 2014 10:25:41 +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>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH v2 05/11] ARM: topology: use new cpu_power interface

On 25 May 2014 15:22, Preeti U Murthy <preeti@...ux.vnet.ibm.com> wrote:
> Hi Vincent,
>
> Why do we have two interfaces arch_scale_freq_power() and
> arch_scale_cpu_power()? Does it make sense to consolidate them now ?
Hi Preeti,

They don't have the same purpose. arch_scale_cpu_power set the max
capacity of your CPU whereas arch_scale_freq_power can be used to give
the current capacity. ARM platform were using arch_scale_freq_power
because it was the only one available for non SMT system but this
induces some misunderstanding and some limitation in the
characterization of a CPUs. This consolidation is a necessary step so
we can now have the max capacity of a CPU and let
arch_scale_freq_power for other purpose (or even remove it if
useless).

Regards,
Vincent

>
> Regards
> Preeti U Murthy
>
>
> On 05/23/2014 09:22 PM, Vincent Guittot wrote:
>> Use the new arch_scale_cpu_power in order to reflect the original capacity of
>> a CPU instead of arch_scale_freq_power which is more linked to a scaling of
>> the capacity linked to the frequency.
>>
>> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
>> ---
>>  arch/arm/kernel/topology.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
>> index 71e1fec..6cc25a8 100644
>> --- a/arch/arm/kernel/topology.c
>> +++ b/arch/arm/kernel/topology.c
>> @@ -42,7 +42,7 @@
>>   */
>>  static DEFINE_PER_CPU(unsigned long, cpu_scale);
>>
>> -unsigned long arch_scale_freq_power(struct sched_domain *sd, int cpu)
>> +unsigned long arch_scale_cpu_power(struct sched_domain *sd, int cpu)
>>  {
>>       return per_cpu(cpu_scale, cpu);
>>  }
>> @@ -166,7 +166,7 @@ static void update_cpu_power(unsigned int cpu)
>>       set_power_scale(cpu, cpu_capacity(cpu) / middle_capacity);
>>
>>       printk(KERN_INFO "CPU%u: update cpu_power %lu\n",
>> -             cpu, arch_scale_freq_power(NULL, cpu));
>> +             cpu, arch_scale_cpu_power(NULL, cpu));
>>  }
>>
>>  #else
>>
>
--
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