Re: a question about p4_clockmod module on Xeon quad core processors

[Xiaoning Ding <dingxn@ymail.com>]

--- On Thu, 1/29/09, Dave Jones <davej@redhat.com> wrote:

> From: Dave Jones <davej@redhat.com>
> Subject: Re: a question about p4_clockmod module on Xeon quad core processors
> To: "Xiaoning Ding" <dingxn@ymail.com>
> Cc: linux-kernel@vger.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
> 
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