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

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Message-ID: <20160209100103.GB5726@in.ibm.com>
Date:	Tue, 9 Feb 2016 15:31:03 +0530
From:	Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
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>,
	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

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>

> 
> Thanks,
> Rafael

--
Thanks and Regards
gautham.