Re: [PATCH 1/5] cpufreq: Use cpumask_copy instead of cpumask_or to copy a mask

[Saravana Kannan]

On 10/12/2015 08:23 PM, Viresh Kumar wrote:
> On 12-10-15, 12:12, Saravana Kannan wrote:
> > >   	if (new_policy) {
> > >   		/* related_cpus should at least include policy->cpus. */
> > > -		cpumask_or(policy->related_cpus, policy->related_cpus, policy->cpus);
> > > +		cpumask_copy(policy->related_cpus, policy->cpus);
> >
> > Again, why? It actually seems wrong. A 4 core cluster could come up
> > with just 2 cores when the policy is added. But the related CPUs
> > would be 4 CPUs.
>
> Firstly, the patch hasn't changed anything at all. related_cpus was
> empty until this point, and orring or setting it with ->cpus will
> result in the same output.

I was under the impression that the CPUfreq drivers were expected to 
fill in related_cpus and the or-ing was a safety net. If that's not the 
case, then this change is fine.

> Secondly, this is what we always wanted. related_cpus should contain
> the mask of all possible CPUs for that cluster.

I think the confusion was that I thought the drivers are supposed to do 
this. If this doesn't mess up other CPUfreq drivers that I'm not 
familiar with, then I don't have concerns.

Can you still explain the why in the commit text though? If it's just 
that related_cpus is always empty and copying is more efficient than 
or-ing, then mention that?

Thanks,
Saravana

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