linux-kernel - Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq

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Message-ID: <20160315213744.GJ6344@twins.programming.kicks-ass.net>
Date:	Tue, 15 Mar 2016 22:37:44 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Michael Turquette <mturquette@...libre.com>
Cc:	rjw@...ysocki.net, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, Juri.Lelli@....com,
	steve.muckle@...aro.org, morten.rasmussen@....com,
	dietmar.eggemann@....com, vincent.guittot@...aro.org,
	Michael Turquette <mturquette+renesas@...libre.com>
Subject: Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity

On Sun, Mar 13, 2016 at 10:22:12PM -0700, Michael Turquette wrote:
> +++ b/kernel/sched/sched.h
> @@ -1368,7 +1368,21 @@ static inline int hrtick_enabled(struct rq *rq)
>  #ifdef CONFIG_SMP
>  extern void sched_avg_update(struct rq *rq);
>  
> -#ifndef arch_scale_freq_capacity

> +#ifdef CONFIG_CPU_FREQ
> +#define arch_scale_freq_capacity cpufreq_scale_freq_capacity
> +#elif !defined(arch_scale_freq_capacity)
>  static __always_inline
>  unsigned long arch_scale_freq_capacity(struct sched_domain *sd, int cpu)
>  {

This could not allow x86 to use the APERF/MPERF thing, so no, can't be
right.

Maybe something like

#ifndef arch_scale_freq_capacity
#ifdef CONFIG_CPU_FREQ
#define arch_scale_freq_capacity	cpufreq_scale_freq_capacity
#else
static __always_inline
unsigned long arch_scale_freq_capacity(..)
{
	return SCHED_CAPACITY_SCALE;
}
#endif
#endif

Which will let the arch override and only falls back to cpufreq if
the arch doesn't do anything.