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

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Message-ID: <50A12565.4070701@calxeda.com>
Date:	Mon, 12 Nov 2012 10:35:49 -0600
From:	Mark Langsdorf <mark.langsdorf@...xeda.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	"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 11/11/2012 10:38 AM, Borislav Petkov wrote:
> On Wed, Nov 07, 2012 at 12:32:43PM -0600, Mark Langsdorf wrote:
>> When collecting stats, if a frequency doesn't match the table, go through
>> the table again with both the search frequency and table values shifted
>> left by 10 bits.
> 
> Why would that second pass succeed?

It's effectively a divide by 1024 and minimizes any jitter in the
measured frequency value.

> And why is this in generic code (I'm assuming this is a Calxeda-specific
> case)?

The function is buried pretty deep in the cpufreq_stat code. It didn't
seem appropriate to make it a function pointer as part of struct
cpufreq_driver.

--Mark Langsdorf
Calxeda, Inc.
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