linux-kernel - Re: [PATCH v3 9/10] cpufreq: sched: Re-introduce cpufreq_update

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Date:	Fri, 4 Mar 2016 22:36:10 +0100
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Steve Muckle <steve.muckle@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Juri Lelli <juri.lelli@....com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Michael Turquette <mturquette@...libre.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v3 9/10] cpufreq: sched: Re-introduce cpufreq_update_util()

On Fri, Mar 4, 2016 at 10:27 PM, Rafael J. Wysocki <rafael@...nel.org> wrote:
> On Fri, Mar 4, 2016 at 10:21 PM, Steve Muckle <steve.muckle@...aro.org> wrote:
>> On 03/04/2016 05:30 AM, Rafael J. Wysocki wrote:
>>> +void cpufreq_update_util(u64 time, unsigned long util, unsigned long max)
>>> +{
>>> +     struct freq_update_hook *hook;
>>> +
>>> +#ifdef CONFIG_LOCKDEP
>>> +     WARN_ON(debug_locks && !rcu_read_lock_sched_held());
>>> +#endif
>>> +
>>> +     hook = rcu_dereference_sched(*this_cpu_ptr(&cpufreq_freq_update_hook));
>>> +     /*
>>> +      * If this isn't inside of an RCU-sched read-side critical section, hook
>>> +      * may become NULL after the check below.
>>> +      */
>>> +     if (hook) {
>>> +             if (hook->update_util)
>>> +                     hook->update_util(hook, time, util, max);
>>> +             else
>>> +                     hook->func(hook, time);
>>> +     }
>>
>> Is it worth having two hook types?
>
> Well, that's why I said "maybe over the top" in the changelog comments. :-)
>
> If we want to isolate the "old" governors from util/max entirely, then yes.
>
> If we don't care that much, then no.
>
> I'm open to both possibilities.

But in the latter case I don't see a particular reason to put the new
governor under kernel/sched/ too and as I wrote in the changelog
comments to patch [10/10], I personally think that it would be cleaner
to keep it under drivers/cpufreq/.

Thanks,
Rafael