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

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Date:	Fri, 4 Mar 2016 22:27:46 +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 10:21 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.

Thanks,
Rafael