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Message-ID: <213679.55387.qm@web59907.mail.ac4.yahoo.com>
Date: Thu, 29 Jan 2009 08:32:41 -0800 (PST)
From: Xiaoning Ding <dingxn@...il.com>
To: Dave Jones <davej@...hat.com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: a question about p4_clockmod module on Xeon quad core processors
--- On Thu, 1/29/09, Dave Jones <davej@...hat.com> wrote:
> From: Dave Jones <davej@...hat.com>
> Subject: Re: a question about p4_clockmod module on Xeon quad core processors
> To: "Xiaoning Ding" <dingxn@...il.com>
> Cc: linux-kernel@...r.kernel.org
> Date: Thursday, January 29, 2009, 2:45 AM
> [please don't top-post]
>
> On Wed, Jan 28, 2009 at 06:06:37PM -0800, Xiaoning Ding
> wrote:
>
> > > > I have tried the p4-clockmod module in
> Linux kernel
> > > 2.6.29 on Xeon 5355 quad-core CPUs with no luck.
> It seems
> > > current p4-clockmod driver still cannot support
> Intel Quad
> > > core processors, right?
> > > >
> > > > I know I can also use acpi-cpufreq. It can
> only scale
> > > down the frequence from 2.67GHz to 2GHz. But I
> need some
> > > lower frequencies for some experiments.
> > >
> > > p4-clockmod doesn't change the processor
> frequency.
> > > Because of common misconceptions like this, the
> user
> > > interface has been removed.
> > >
> > > In 2.6.29, the clock modulation code is called
> directly
> > > from ACPI
> > > whenever thermal events indicate that throttling
> is
> > > necessary.
> > >
> > Thanks for the correction.
> > My experiments need to reduce CPU speed. However, I
> can only reduce the speed by about 30% (from 2.67GHz to
> 2GHz) with ACPI. That is not enough for the experiments.
>
> The ACPI P-states are nearly always correct, so you
> won't be
> able to go below 2GHz on this system.
That's true for changing P-States with ACPI. But I can still get slower speed with clock modulation, right?
> > p4-clockmod has not been removed from 2.6.29. It is
> under the same directory as acpi-cpufreq
> (arch/x86/kernel/cpu/cpufreq). So I thought it was an
> alternative approach. But I could not get it loaded.
>
> The driver is present, the _user interface_ has been
> removed.
The module cannot loaded on Xeon 5355. If I can load it, I hope I can find a method to use it.
> Dave
>
> --
> http://www.codemonkey.org.uk
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