linux-kernel - Re: [PATCH 0/3] cpufreq: Replace timers with utilization update callbacks

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Date:	Wed, 10 Feb 2016 14:03:15 +0000
From:	Juri Lelli <juri.lelli@....com>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Steve Muckle <steve.muckle@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 0/3] cpufreq: Replace timers with utilization update
 callbacks

On 10/02/16 14:23, Rafael J. Wysocki wrote:
> On Wed, Feb 10, 2016 at 1:33 PM, Juri Lelli <juri.lelli@....com> wrote:
> > Hi Rafael,
> >
> > On 09/02/16 21:05, Rafael J. Wysocki wrote:
> >
> > [...]
> >
> >> +/**
> >> + * cpufreq_update_util - Take a note about CPU utilization changes.
> >> + * @util: Current utilization.
> >> + * @max: Utilization ceiling.
> >> + *
> >> + * This function is called by the scheduler on every invocation of
> >> + * update_load_avg() on the CPU whose utilization is being updated.
> >> + */
> >> +void cpufreq_update_util(unsigned long util, unsigned long max)
> >> +{
> >> +     struct update_util_data *data;
> >> +
> >> +     rcu_read_lock();
> >> +
> >> +     data = rcu_dereference(*this_cpu_ptr(&cpufreq_update_util_data));
> >> +     if (data && data->func)
> >> +             data->func(data, cpu_clock(smp_processor_id()), util, max);
> >
> > Are util and max used anywhere?
> 
> They aren't yet, but they will be.
> 
> Maybe not in this cycle (it it takes too much time to integrate the
> preliminary changes), but we definitely are going to use those
> numbers.
> 

Oh OK. However, I was under the impression that this set was only
proposing a way to get rid of timers and use the scheduler as heartbeat
for cpufreq governors. The governors' sample based approach wouldn't
change, though. Am I wrong in assuming this?

Also, is linux-pm/bleeding-edge the one I want to fetch to try this set
out?

Thanks,

- Juri