Re: [PATCH 2/2] sched/cpufreq: Update schedutil's DVFS request to reach the boost frequencies

[Sibi Sankar]

On 8/6/2026 8:39 PM, Vincent Guittot wrote:
> On Thu, 6 Aug 2026 at 06:42, Sibi Sankar <sibi.sankar@xxxxxxxxxxxxxxxx> wrote:
> > capacity_freq_ref, exposed to schedutil via get_capacity_ref_freq(),
> > was introduced by commit 9942cb22ea45 ("sched/topology: Add a new
> > arch_scale_freq_ref() method") as a fixed anchor that does not move at
> > runtime. However, schedutil uses that same fixed anchor as the reference
> > plugged into map_util_freq() which saturates exactly at capacity_freq_ref.
> >
> > As a result, a system with cpufreq boost enabled effectively never runs at
> > boost frequencies under schedutil-governed load. Fix this by plugging in
> > policy-max into the map_util_freq equation, so that the DVFS requests
> > translates to the actual cpufreq driver ceiling.
> >
> > Signed-off-by: Sibi Sankar <sibi.sankar@xxxxxxxxxxxxxxxx>
> > ---
> >   kernel/sched/cpufreq_schedutil.c | 13 ++++++++++---
> >   1 file changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > index a1782755efcc..dcefbeaa0702 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -195,10 +195,17 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
> >                                    unsigned long util, unsigned long max)
> >   {
> >          struct cpufreq_policy *policy = sg_policy->policy;
> > -       unsigned int freq;
> > +       unsigned int freq, ref;
> >
> > -       freq = get_capacity_ref_freq(policy);
> > -       freq = map_util_freq(util, freq, max);
> > +       ref = get_capacity_ref_freq(policy);
> > +
> > +       /*
> > +        * That fixed anchor governs how utilization is interpreted, but
> > +        * the DVFS request is free to target the current policy ceiling.
> > +        * Using ref alone would saturate the util->freq map at ref so
> > +        * use policy->max to reach boost frequencies.
> > +        */
> > +       freq = map_util_freq(util, max(ref, READ_ONCE(policy->max)), max);
> But this is wrong because arch_scale_freq_ref is the freq that has
> been used when setting the capacity of the cpu and is there to make
> sure that the translation between freq <-> capacity is correct and
> consistent whatever happens later on the freq table of cpufreq. This
> ensures that utilization tracking remains correct vs other CPUS and
> prevents or minimizes utilization oscillation, which triggers other
> problems
>
> Either we enable the utilization value to go above CPU's capacity when
> we transmit it to cpufreq (and above SCHED_CAPACITY_SCALE which could
> trigger a number of problem while computing pelt)
> Or, you take into account the boost freq when setting cpu's capacity
> and associated capacity_freq_ref at boot even if not enabled. With
> cpufreq pressure feature and the policy->max (not  cpuinfo_max_freq)
> correctly updated with a freq_qos_update_request when boost is
> enabled/disabled, the scheduler and pelt should handle that correctly
> as we normaly take into account cpufreq_pressure everywhere in
> scheduler.

Thanks for your inputs! Ack, will try out the latter since it appears to 
be the
right way to address this.

> >          if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
> >                  return sg_policy->next_freq;
> > --
> > 2.34.1