linux-kernel - Re: [Acpi4asus-user] [PATCH 1/1] cpufreq: eeepc 900 frequency scaling driver

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Message-ID: <20090405102057.GA14089@srcf.ucam.org>
Date:	Sun, 5 Apr 2009 11:20:57 +0100
From:	Matthew Garrett <mjg@...hat.com>
To:	Corentin Chary <corentin.chary@...il.com>
Cc:	Cristiano Prisciandaro <cristiano.p@...net.ch>,
	Thomas Renninger <trenn@...e.de>,
	Dave Jones <davej@...hat.com>,
	acpi4asus-user@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	cpufreq@...r.kernel.org, Tom Hughes <tom@...pton.nu>,
	linux acpi <linux-acpi@...r.kernel.org>,
	Francesco Lattanzio <f.lattanzio@...ail.it>,
	Grigori Goronzy <greg@...wn.ath.cx>
Subject: Re: [Acpi4asus-user] [PATCH 1/1] cpufreq: eeepc 900 frequency scaling driver

On Sun, Apr 05, 2009 at 09:43:40AM +0200, Corentin Chary wrote:
> >> Could it happen that upcoming machines provide this interface (the two ACPI
> >> functions) and also can do real CPU frequency/volt switching, e.g. via
> >> acpi-cpufreq?
> >
> > Probably this interface is a solution specific to machines based on the
> > celeron M: I don't even know if other 'old' models provide the same
> > interface.
> 
> Hi,
> We I just received another patch for that (adding a cpufv file in
> sysfs) and I don't really know what to do.
> 
> As Grigori Goronzy said, using cpufreq in not a good idea:

I'm not sure I agree. It's clear that ondemand and conservative aren't 
sensible choices with the driver, but beyond that...

> > 3) It looks like it is impossible to use more than one cpufreq driver
> > per CPU. This effectively means you can either use the regular ACPI
> > frequency scaling, which switches between multipliers, or SHE. That's
> > unacceptable. SHE is not intended to replace the regular frequency
> > scaling, but to complement it.

I don't think there's a terribly good reason to use the SHE methods if 
the CPU supports speedstep. 945 will automatically drop the frontside 
bus in the deepest P states. I'd be surprised if it gave any real world 
benefits on the atom based systems.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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