linux-kernel - Re: [PATCH 2/6] sched/fair: Convert arch_scale_cpu

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Message-ID: <CAKfTPtBkrpHVKZ3kx9JrvtYoD6rkDD8c2=p0hJ39U3SBBe5fSQ@mail.gmail.com>
Date:	Fri, 11 Sep 2015 16:45:49 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Dietmar Eggemann <dietmar.eggemann@....com>
Cc:	Morten Rasmussen <Morten.Rasmussen@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Yuyang Du <yuyang.du@...el.com>,
	Michael Turquette <mturquette@...libre.com>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	Juri Lelli <Juri.Lelli@....com>,
	Sai Charan Gurrappadi <sgurrappadi@...dia.com>,
	"pang.xunlei@....com.cn" <pang.xunlei@....com.cn>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] sched/fair: Convert arch_scale_cpu_capacity() from
 weak function to #define

On 11 September 2015 at 15:21, Dietmar Eggemann
<dietmar.eggemann@....com> wrote:
> On 04/09/15 08:26, Vincent Guittot wrote:
>> On 3 September 2015 at 21:58, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>
> [...]
>
>> So, with the patch below that updates the arm definition of
>> arch_scale_cpu_capacity, you can add my Acked-by: Vincent Guittot
>> <vincent.guittot@...aro.org> on this patch and the additional one
>> below
>
> My tests on ARM TC2 (only the 2 A15's) show that the influence of the
> non-default arch_scale_cpu_capacity function in
> arch/arm/kernel/topology.c and with it the extra function call to it
> from __update_load_avg() has no measurable influence on performance:
>
> perf stat --null --repeat 10 -- perf bench sched messaging --g 50 -l 200
>
> - default arch_scale_cpu_capacity function [kernel/sched/sched.h]
>
> 16.006976251 seconds time elapsed ( +- 0.29% )
> 16.063814914 seconds time elapsed ( +- 0.37% )
> 16.088199252 seconds time elapsed ( +- 0.39% )
>
> - arch_scale_cpu_capacity function [arch/arm/kernel/topology.c]
>
> 15.945975308 seconds time elapsed ( +- 0.10% )
> 16.131203074 seconds time elapsed ( +- 0.21% )
> 16.108302562 seconds time elapsed ( +- 0.41% )
>
> If I force the function to be inline, the result is slightly worse:
>
> - arch_scale_cpu_capacity function [arch/arm/include/asm/topology.h]
>
> 16.122545216 seconds time elapsed ( +- 0.09% )
> 16.285819258 seconds time elapsed ( +- 0.35% )
> 16.157454024 seconds time elapsed ( +- 0.15% )
>
> So I think we can connect the arch_scale_cpu_capacity function
> [arch/arm/kernel/topology.c] to the CFS scheduler for ARCH=arm so that
> people get cpu scale different to 1024 on arm big.little machines w/
> A15/A7 in case the specify clock-frequency properties in their dtb file.
>
> Can we still have your 'Acked-by' for this patch and 3/6 even though we
> now scale weight (by frequency) and scale_freq (by cpu) instead of the
> time related values (delta_w, contrib, delta)?

Yes, Please add my Acked-by

Vincent

>
> Thanks,
>
> -- Dietmar
>
>>
>> Regards,
>> Vincent
>>
>>>
>>> To connect the cpu invariant engine (scale_cpu_capacity()
>>> [arch/arm/kernel/topology.c]) with the scheduler, something like this is
>>> missing:
>>>
>>> diff --git a/arch/arm/include/asm/topology.h b/arch/arm/include/asm/topology.h
>>> index 370f7a732900..17c6b3243196 100644
>>> --- a/arch/arm/include/asm/topology.h
>>> +++ b/arch/arm/include/asm/topology.h
>>> @@ -24,6 +24,10 @@ void init_cpu_topology(void);
>>>  void store_cpu_topology(unsigned int cpuid);
>>>  const struct cpumask *cpu_coregroup_mask(int cpu);
>>>
>>> +#define arch_scale_cpu_capacity scale_cpu_capacity
>>> +struct sched_domain;
>>> +extern unsigned long scale_cpu_capacity(struct sched_domain *sd, int cpu);
>>> +
>>>  #else
>>>
>>>  static inline void init_cpu_topology(void) { }
>>> diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
>>> index 08b7847bf912..907e0d2d9b82 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_cpu_capacity(struct sched_domain *sd, int cpu)
>>> +unsigned long scale_cpu_capacity(struct sched_domain *sd, int cpu)
>>>  {
>>>         return per_cpu(cpu_scale, cpu);
>>>  }
>>> @@ -166,7 +166,7 @@ static void update_cpu_capacity(unsigned int cpu)
>>>         set_capacity_scale(cpu, cpu_capacity(cpu) / middle_capacity);
>>>
>>>         pr_info("CPU%u: update cpu_capacity %lu\n",
>>> -               cpu, arch_scale_cpu_capacity(NULL, cpu));
>>> +               cpu, scale_cpu_capacity(NULL, cpu));
>>>  }
>>>
>>> -- Dietmar
>>>
>>> [...]
>
--
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