linux-kernel - Re: [PATCH 4/5] ACPI: Do cpufreq clamping for throttling per package v2

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Message-ID: <4F399D19.9090904@kernel.org>
Date:	Mon, 13 Feb 2012 18:30:33 -0500
From:	Len Brown <lenb@...nel.org>
To:	Matthew Garrett <mjg59@...f.ucam.org>
CC:	Andi Kleen <andi@...stfloor.org>, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 4/5] ACPI: Do cpufreq clamping for throttling per package
 v2

On 02/06/2012 11:31 AM, Matthew Garrett wrote:

> On Mon, Feb 06, 2012 at 08:17:11AM -0800, Andi Kleen wrote:
>> +#define reduction_pctg(cpu) \
>> +	per_cpu(cpufreq_thermal_reduction_pctg, phys_package_first_cpu(cpu))
> 
> I don't like using percentages here - we end up with the potential for 
> several percentages to end up mapping to the same P state.


Does it matter?

> I've sent a

> patch that replaces the percentage code with just stepping through P 
> states instead. But otherwise, yes, this seems sensible. An open 
> question is whether we should be doing the same on _PPC notifications. 
> There's some vague evidence that Windows does.

If you stepped by P-states, then you behave entirely differently
on a machine with many P-states vs a machine with few P-states.

There is code floating about that exposes every 100 MHz step on SNB
and later as a P-state -- you can have quite a few...

thanks,
-Len Brown, Intel Open Source Technology Center


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