Re: [RFC PATCH v3 1/2] cpufreq: change '.set_boost' to act on only one policy

[Viresh Kumar]

On 20-05-20, 12:36, Rafael J. Wysocki wrote:
> On Wed, May 20, 2020 at 6:59 AM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> >
> > On 19-05-20, 19:41, Xiongfeng Wang wrote:
> > > Macro 'for_each_active_policy()' is defined internally. To avoid some
> > > cpufreq driver needing this macro to iterate over all the policies in
> > > '.set_boost' callback, we redefine '.set_boost' to act on only one
> > > policy and pass the policy as an argument.
> > > 'cpufreq_boost_trigger_state()' iterate over all the policies to set
> > > boost for the system. This is preparation for adding SW BOOST support
> > > for CPPC.
> > >
> > > Signed-off-by: Xiongfeng Wang <wangxiongfeng2@xxxxxxxxxx>
> > > ---
> > >  drivers/cpufreq/acpi-cpufreq.c |  4 ++--
> > >  drivers/cpufreq/cpufreq.c      | 53 +++++++++++++++++++++---------------------
> > >  include/linux/cpufreq.h        |  2 +-
> > >  3 files changed, 30 insertions(+), 29 deletions(-)
> > >
> > > diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
> > > index 289e8ce..b0a9eb5 100644
> > > --- a/drivers/cpufreq/acpi-cpufreq.c
> > > +++ b/drivers/cpufreq/acpi-cpufreq.c
> > > @@ -126,7 +126,7 @@ static void boost_set_msr_each(void *p_en)
> > >       boost_set_msr(enable);
> > >  }
> > >
> > > -static int set_boost(int val)
> > > +static int set_boost(struct cpufreq_policy *policy, int val)
> > >  {
> > >       get_online_cpus();
> > >       on_each_cpu(boost_set_msr_each, (void *)(long)val, 1);
> >
> > I think (Rafael can confirm), that you need to update this as well. You don't
> > need to run for each cpu now, but for each CPU in the policy.
> 
> Right, the caller will iterate over policies.
> 
> Accordingly, the CPU hotplug locking needs to go to the caller too.

Hmm, why is that required ? Can't we call boost_set_msr_each() for all
CPUs of a policy under the locks ? And then let the next call take the
lock again ? I thought we don't want a CPU to disappear while we are
trying to run boost_set_msr_each() for it (or miss one that just got
added) and that should work with the locks being there in this routine.

-- 
viresh