Re: [PATCH V3 2/9] cpufreq: Use transition_delay_us for legacy governors as well

From: Peter Zijlstra
Date: Mon Jul 24 2017 - 12:17:40 EST


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@xxxxxxxxxx>
> ---
> 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?