Re: [PATCH] cpufreq: Rebuild sched-domains when removing cpufreq driver

[Pierre Gondois]

Hello Viresh, Dietmar,

On 9/28/23 09:18, Viresh Kumar wrote:
> On 18-09-23, 13:29, Pierre Gondois wrote:
> > The Energy Aware Scheduler (EAS) relies on the schedutil governor.
> > When moving to/from the schedutil governor, sched domains must be
> > rebuilt to allow re-evaluating the enablement conditions of EAS.
> > This is done through sched_cpufreq_governor_change().
> >
> > Having a cpufreq governor assumes having a cpufreq driver running.
> > Inserting/removing a cpufreq driver should trigger a re-evaluation
> > of EAS enablement conditions, avoiding to see EAS enabled when
> > removing a running cpufreq driver.
> >
> > Add a sched_cpufreq_governor_change() call in cpufreq driver removal
> > path.
> >
> > Signed-off-by: Pierre Gondois <pierre.gondois@xxxxxxx>
> > ---
> >   drivers/cpufreq/cpufreq.c | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index 60ed89000e82..0a4979c34fd1 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -1673,6 +1673,8 @@ static void __cpufreq_offline(unsigned int cpu, struct cpufreq_policy *policy)
> >   		cpufreq_driver->exit(policy);
> >   		policy->freq_table = NULL;
> >   	}
> > +
> > +	sched_cpufreq_governor_change(policy, policy->governor);
>
> This is called from many paths. Consider using cpufreq_remove_dev() instead,
> before the policy is freed.

Another solution would be to call sched_cpufreq_governor_change()
from cpufreq_schedutil's init()/exit() callbacks. This would make
more sense as EAS/schedutil cpufreq are tightly bound, and it would
allow to cover all the possible paths.

When tried locally, it seems to cover all scenarios:
- insmod/rmmod a cpufreq driver
- changing the governor policy
- offlining all the CPUs of a pd

Dietmar:
The function would be static to cpufreq_schedutil, and the name can
be changed at the same time to (unless you think of a better name ?):
  static void sugov_check_eas_state(void);

Regards,
Pierre