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Message-ID: <561D5A03.3010204@codeaurora.org>
Date: Tue, 13 Oct 2015 12:22:43 -0700
From: Saravana Kannan <skannan@...eaurora.org>
To: Viresh Kumar <viresh.kumar@...aro.org>
CC: Rafael Wysocki <rjw@...ysocki.net>, linaro-kernel@...ts.linaro.org,
linux-pm@...r.kernel.org, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/5] cpufreq: Use cpumask_copy instead of cpumask_or to
copy a mask
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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