Re: About CPU hot-plug stress test failed in cpufreq driver

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Tuesday, December 10, 2019 9:57:44 AM CET Viresh Kumar wrote:
> On 10-12-19, 09:50, Rafael J. Wysocki wrote:
> > Index: linux-pm/include/linux/cpufreq.h
> > ===================================================================
> > --- linux-pm.orig/include/linux/cpufreq.h
> > +++ linux-pm/include/linux/cpufreq.h
> > @@ -599,11 +599,13 @@ static inline bool cpufreq_this_cpu_can_
> >  {
> >  	/*
> >  	 * Allow remote callbacks if:
> > -	 * - dvfs_possible_from_any_cpu flag is set
> >  	 * - the local and remote CPUs share cpufreq policy
> > +	 * - dvfs_possible_from_any_cpu flag is set and the CPU running the
> > +	 *   code is not going offline.
> >  	 */
> > -	return policy->dvfs_possible_from_any_cpu ||
> > -		cpumask_test_cpu(smp_processor_id(), policy->cpus);
> > +	return cpumask_test_cpu(smp_processor_id(), policy->cpus) ||
> > +		(policy->dvfs_possible_from_any_cpu &&
> > +		 !cpumask_test_cpu(smp_processor_id(), policy->related_cpus));
> 
> This isn't enough as you are assuming that only a CPU from policy->related_cpus
> can do remote processing. On a ARM platform (like Qcom's Krait, octa-core), all
> 8 CPUs have separate policies as they don't share clock lines. Though they can
> still do remote processing for each other as the clk registers are common.
> 
> Also policy->related_cpus can anyway update frequency for the policy even if
> dvfs_possible_from_any_cpu is set to false.

I know, see

https://lore.kernel.org/linux-pm/CAJZ5v0h0934-VBODZZJ8gEG2byuhQ+bomoCuTmmQZOBtqu5bKQ@mail.gmail.com/T/#mccadfdc557468072ab6c5525601a71d60070e99b