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SubjectRe: [PATCH 2/2] cpufreq: schedutil: consolidate capacity margin calculation
On Mon, Sep 25, 2017 at 02:55:07PM +0100, Patrick Bellasi wrote:
> On 23-Sep 07:04, Leo Yan wrote:
> > Scheduler CFS class has variable 'capacity_margin' to calculate the
> > capacity margin, and schedutil governor also needs to compensate the
> > same margin for frequency tipping point. Below are formulas used in
> > CFS class and schedutil governor separately:
> >
> > CFS: U` = U * capacity_margin / 1024 = U * 1.25
> > Schedutil: U` = U + U >> 2 = U + U * 0.25 = U * 1.25
> >
> > This patch consolidates the capacity margin calculation so let
> > schedutil to use same formula with CFS class. As result this can avoid
> > the mismatch issue between schedutil and CFS class after change
> > 'capacity_margin' to other values.
> >
> > Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> > Cc: Morten Rasmussen <morten.rasmussen@arm.com>
> > Cc: Chris Redpath <Chris.Redpath@arm.com>
> > Cc: Joel Fernandes <joelaf@google.com>
> > Cc: Vincent Guittot <vincent.guittot@linaro.org>
> > Signed-off-by: Leo Yan <leo.yan@linaro.org>
> > ---
> > kernel/sched/cpufreq_schedutil.c | 5 +++--
> > kernel/sched/sched.h | 1 +
> > 2 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > index 9209d83..067abbe 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -155,7 +155,8 @@ static void sugov_update_commit(struct sugov_policy *sg_policy, u64 time,
> > *
> > * next_freq = C * curr_freq * util_raw / max
> > *
> > - * Take C = 1.25 for the frequency tipping point at (util / max) = 0.8.
> > + * Take C = capacity_margin / 1024 = 1.25, so it's for the frequency tipping
> > + * point at (util / max) = 0.8.
> > *
> > * The lowest driver-supported frequency which is equal or greater than the raw
> > * next_freq (as calculated above) is returned, subject to policy min/max and
> > @@ -168,7 +169,7 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
> > unsigned int freq = arch_scale_freq_invariant() ?
> > policy->cpuinfo.max_freq : policy->cur;
> >
> > - freq = (freq + (freq >> 2)) * util / max;
> > + freq = (freq * capacity_margin / 1024) * util / max;
>
> The compiler should be smart enough but perhaps you can better use:
>
> freq *= (capacity_margin >> SCHED_CAPACITY_SHIFT));
> freq *= util / max;

Thanks for the suggestion. The '*=' has low precedence than other
operators, will fix as below:

freq = freq * capacity_margin >> SCHED_CAPACITY_SHIFT;
freq = freq * util / max;

> > if (freq == sg_policy->cached_raw_freq && sg_policy->next_freq != UINT_MAX)
> > return sg_policy->next_freq;
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index 14db76c..cf75bdc 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -52,6 +52,7 @@ struct cpuidle_state;
> > #define TASK_ON_RQ_MIGRATING 2
> >
> > extern __read_mostly int scheduler_running;
> > +extern unsigned int capacity_margin __read_mostly;
> >
> > extern unsigned long calc_load_update;
> > extern atomic_long_t calc_load_tasks;
> > --
> > 2.7.4
> >
>
> --
> #include <best/regards.h>
>
> Patrick Bellasi

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