linux-kernel - Re: [PATCH V3 2/9] cpufreq: Use transition_delay

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Date:   Mon, 24 Jul 2017 18:17:19 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Rafael Wysocki <rjw@...ysocki.net>, Ingo Molnar <mingo@...hat.com>,
        linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux@...inikbrodowski.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 2/9] cpufreq: Use transition_delay_us for legacy
 governors as well

On Wed, Jul 19, 2017 at 03:42:42PM +0530, Viresh Kumar wrote:
> The policy->transition_delay_us field is used only by the schedutil
> governor currently, and this field describes how fast the driver wants
> the cpufreq governor to change CPUs frequency. It should rather be a
> common thing across all governors, as it doesn't have any schedutil
> dependency here.
> 
> Create a new helper cpufreq_policy_transition_delay_us() to get the
> transition delay across all governors.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  drivers/cpufreq/cpufreq.c          | 15 +++++++++++++++
>  drivers/cpufreq/cpufreq_governor.c |  9 +--------
>  include/linux/cpufreq.h            |  1 +
>  kernel/sched/cpufreq_schedutil.c   | 11 +----------
>  4 files changed, 18 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 9bf97a366029..c426d21822f7 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -524,6 +524,21 @@ unsigned int cpufreq_driver_resolve_freq(struct cpufreq_policy *policy,
>  }
>  EXPORT_SYMBOL_GPL(cpufreq_driver_resolve_freq);
>  
> +unsigned int cpufreq_policy_transition_delay_us(struct cpufreq_policy *policy)
> +{
> +	unsigned int latency;
> +
> +	if (policy->transition_delay_us)
> +		return policy->transition_delay_us;
> +
> +	latency = policy->cpuinfo.transition_latency / NSEC_PER_USEC;
> +	if (latency)
> +		return latency * LATENCY_MULTIPLIER;
> +
> +	return LATENCY_MULTIPLIER;
> +}
> +EXPORT_SYMBOL_GPL(cpufreq_policy_transition_delay_us);

I realize you're just moving code about, but _why_ are we doing that
division?