On 24-07-17, 18:17, Peter Zijlstra wrote:
> 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.ku...@linaro.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?
We are doing division by NSEC_PER_USEC because the values of
sampling_rate and rate_limit_us are in us, while transition_latency is
in ns.
We shouldn't be breaking the userspace ABI and so if we want, we can
actually make transition_latency be stored in us instead.
Though I am not sure why are we multiplying with LATENCY_MULTIPLIER
(1000) as that seems to be a huge value.
--
viresh
