linux-kernel - Re: [PATCH 3/6 v4] cpufreq: tolerate inexact values when collecting stats

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Message-ID: <3756540.1nyvqzWibd@vostro.rjw.lan>
Date:	Sat, 24 Nov 2012 11:05:09 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Mark Langsdorf <mark.langsdorf@...xeda.com>
Cc:	Borislav Petkov <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	MyungJoo Ham <myungjoo.ham@...il.com>
Subject: Re: [PATCH 3/6 v4] cpufreq: tolerate inexact values when collecting stats

On Saturday, November 17, 2012 03:50:48 PM Borislav Petkov wrote:
> On Tue, Nov 13, 2012 at 02:13:38PM -0500, Mark Langsdorf wrote:
> > Although cpufreq_driver has a flag field, no part of cpufreq_driver
> > is directly passed to the cpufreq_stat code. Only cpufreq_policy
> > is. It's cleaner to do passes of the while loop than to copy the
> > cpufreq_driver.flag field into cpufreq_policy and then store it again
> > in cpufreq_stats.
> 
> That maybe so but this newly added loop which is only Calxeda-relevant
> is called in cpufreq_stat_notifier_trans, which is the frequency change
> notifier call, AFAICT.
> 
> So each cpufreq driver will be paying that small and needless penalty
> now for nothing and on each frequency change. Which adds to the
> kernel-wide bloat and we absolutely don't want that.
> 
> So you probably need to find a slick way of detecting calxeda hw
> somewhere along the init path of cpufreq_stats_init and set a
> hw-specific flag instead of adding that cost to each driver.

Mark, I suppose you'd like me to take this series for v3.8, but the above
comment from Boris has to be addressed for that.

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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