linux-kernel - Re: [PATCH 3/3 v5] cpufreq: governor: Replace timers with utilization update callbacks

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Date:	Tue, 9 Feb 2016 19:49:33 +0100
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	ego@...ux.vnet.ibm.com
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	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>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Juri Lelli <juri.lelli@....com>,
	Steve Muckle <steve.muckle@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3/3 v5] cpufreq: governor: Replace timers with utilization
 update callbacks

On Tue, Feb 9, 2016 at 11:01 AM, Gautham R Shenoy
<ego@...ux.vnet.ibm.com> wrote:
> Hello Rafael,
>
> On Sun, Feb 07, 2016 at 03:50:31PM +0100, 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.
>
> I tested this patch series (including v5 of PATCH 3) on POWER with
> Viresh's CPUFreq test suite. I didn't see any issues with the
> patchset except for a lockdep splat involving "s_active" and
> "od_dbs_cdata.mutex", which was also observed on 4.5-rc3 and which
> was fixed by Viresh's recent patches.
>
> With a kernbench run, there were no regression when compared to 4.5-rc3.
>
> FWIW, Tested-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>

Thank you!