linux-kernel - Re: [PATCH 3/3 v4] cpufreq: governor: Replace timers with utilization update callbacks

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Date:	Sun, 07 Feb 2016 15:36:02 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Juri Lelli <juri.lelli@....com>,
	Steve Muckle <steve.muckle@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3/3 v4] cpufreq: governor: Replace timers with utilization update callbacks

On Sunday, February 07, 2016 02:50:19 PM Viresh Kumar wrote:
> On 06-02-16, 04:40, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > 
> > Instead of using a per-CPU deferrable timer for queuing up governor
> > work items, register a utilization update callback that will be
> > invoked from the scheduler on utilization changes.
> > 
> > The sampling rate is still the same as what was used for the
> > deferrable timers and the added irq_work overhead should be offset by
> > the eliminated timers overhead, so in theory the functional impact of
> > this patch should not be significant.
> > 
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > ---
> > 
> > Updated after the recent discussion with Viresh.
> > 
> > Changes from v3:
> > - The completion used for irq_work synchronization replaced with irq_work_sync()
> >   in gov_cancel_work().
> > - update_sampling_rate() now modifies shared->sample_delay_ns for all CPUs
> >   where it matters directly with a big fat comment explaining why this is
> >   actually OK.
> > - The above means the time_stamp field in struct cpu_common_dbs_info is not
> >   necessary any more, so it is dropped.
> > - A build error for !CONFIG_SMP is addressed (hopefully effectively).
> > 
> > This version was lightly tested on an x86 laptop.
> 
> Awesome work Rafael, this looks really good now.
> 
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

Thanks!

I have one small update, though.  Namely, it is more logical to initialize
irq_work along with doing INIT_WORK() on the main work item.

I'll send it in a while.

Thanks,
Rafael