Re: [PATCH V3 2/3] cpufreq: intel_pstate: Migrate away from ->stop_cpu() callback

[Viresh Kumar]

On 18-06-21, 14:00, Rafael J. Wysocki wrote:
> On Fri, Jun 18, 2021 at 5:22 AM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> >
> > commit 367dc4aa932b ("cpufreq: Add stop CPU callback to cpufreq_driver
> > interface") added the stop_cpu() callback to allow the drivers to do
> > clean up before the CPU is completely down and its state can't be
> > modified.
> >
> > At that time the CPU hotplug framework used to call the cpufreq core's
> > registered notifier for different events like CPU_DOWN_PREPARE and
> > CPU_POST_DEAD. The stop_cpu() callback was called during the
> > CPU_DOWN_PREPARE event.
> >
> > This is no longer the case, cpuhp_cpufreq_offline() is called only once
> > by the CPU hotplug core now and we don't really need to separately
> > call stop_cpu() for cpufreq drivers.
> >
> > Migrate to using the exit() and offline() callbacks instead of
> > stop_cpu().
> >
> > We need to clear util hook from both the callbacks, exit() and
> > offline(), since it is possible that only exit() gets called sometimes
> > (specially on errors) or both get called at other times.
> > intel_pstate_clear_update_util_hook() anyway have enough protection in
> > place if it gets called a second time and will return early then.
> >
> > Cc: Dirk Brandewie <dirk.brandewie@xxxxxxxxx>
> > Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> > ---
> > V2->V3:
> > - Update intel_pstate_cpu_offline() as well.
> > - Improved commit log.
> >
> >  drivers/cpufreq/intel_pstate.c | 12 ++++--------
> >  1 file changed, 4 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> > index 0e69dffd5a76..8f8a2d9d7daa 100644
> > --- a/drivers/cpufreq/intel_pstate.c
> > +++ b/drivers/cpufreq/intel_pstate.c
> > @@ -2335,6 +2335,8 @@ static int intel_pstate_cpu_offline(struct cpufreq_policy *policy)
> >
> >         pr_debug("CPU %d going offline\n", cpu->cpu);
> >
> > +       intel_pstate_clear_update_util_hook(policy->cpu);
> > +
> >         if (cpu->suspended)
> >                 return 0;
> >
> > @@ -2374,17 +2376,12 @@ static int intel_pstate_cpu_online(struct cpufreq_policy *policy)
> >         return 0;
> >  }
> >
> > -static void intel_pstate_stop_cpu(struct cpufreq_policy *policy)
> > -{
> > -       pr_debug("CPU %d stopping\n", policy->cpu);
> > -
> > -       intel_pstate_clear_update_util_hook(policy->cpu);
> > -}
> > -
> >  static int intel_pstate_cpu_exit(struct cpufreq_policy *policy)
> >  {
> >         pr_debug("CPU %d exiting\n", policy->cpu);
> >
> > +       intel_pstate_clear_update_util_hook(policy->cpu);
> 
> This change is not needed now, because ->offline always runs before
> ->exit if present.

Not necessarily, we don't call ->offline() for many error paths in
cpufreq_online(). offline() only comes into play after driver is registered
properly once.

-- 
viresh