linux-kernel - Re: [PATCH 5/5] cpufreq: Add support for actual freq

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Message-ID: <20100323144152.GA17587@isilmar.linta.de>
Date:	Tue, 23 Mar 2010 15:41:52 +0100
From:	Dominik Brodowski <linux@...inikbrodowski.net>
To:	Borislav Petkov <bp@...64.org>
Cc:	Thomas Renninger <trenn@...e.de>, akpm@...ux-foundation.org,
	davej@...hat.com, cpufreq@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, lenb@...nel.org
Subject: Re: [PATCH 5/5] cpufreq: Add support for actual freq

Hey,

On Tue, Mar 23, 2010 at 03:23:49PM +0100, Borislav Petkov wrote:
> > scaling_cur freq should show the frequency the kernel/cpufreq
> > subsystem thinks it's in.
> 
> Well, we have also
> /sys/devices/system/cpu/cpu<NUM>/cpufreq/cpuinfo_cur_freq and it reads
> also policy->cur.

No. cpuinfo_cur_freq calls __cpufreq_get() which itself calls the driver's
->get() callback, which is exactly for determining the current frequency. I
assume CPUFREQ_CONST_LOOP is set, else we'd get into trouble; but as long as
that's the case I see no problem in using ->get() / cpuinfo_cur_freq to read
out the current actual frequency.

> Why not show the actual frequency in scaling_cur_freq then?

Quoting Documentation/cpu-freq/user-guide.txt :

cpuinfo_cur_freq :              Current frequency of the CPU as obtained from
                                the hardware, in KHz. This is the frequency
                                the CPU actually runs at.

scaling_cur_freq :              Current frequency of the CPU as determined by
                                the governor and cpufreq core, in KHz. This is
                                the frequency the kernel thinks the CPU runs
                                at.

So scaling_cur_freq may not be mis-used for this; cpuinfo_cur_freq may be
used for it, though. IMVHO.

Best,
	Dominik
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