linux-kernel - Re: [PATCH] x86: limit mwait

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Date:	Thu, 05 Apr 2007 14:19:33 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	aherrman@...or.de
CC:	Andi Kleen <ak@...e.de>, linux-kernel@...r.kernel.org,
	andreas.herrmann3@....com
Subject: Re: [PATCH] x86: limit mwait_idle to Intel CPUs

aherrman@...or.de wrote:
> 
>> The ones in /proc/cpuinfo are cooked values anyway; there is plenty of 
>> history to that effect.
> 
> I don't know this history. And I don't care.
> I thought /proc/cpuinfo should show an (almost) complete list
> of CPU features. If this is not the case it's a pity.
> 

It's a list of features which are implemented and working, as far as 
they make sense.  In other words, it's *Linux* concept of the feature 
set of the CPU.

>> I would agree with Andi that if as far as Linux is concerned mwait is 
>> unusable on AMD Fam10 processors, then the CPU detection code should 
>> turn this bit off on AMD Fam10 processors.
> 
> And finally I was not aware that you and Andi think of monitor/mwait
> as a synonym for Intel's native C-States.
> 
> So I guess, what you really want is that for AMD CPUs the
> monitor-flag (aka native C-state-flag) gets removed.
> 
> And if somedays another use case for monitor/mwait appears, the flag
> has to be reintroduced for AMD CPUs.
> 
> Fine with me.
> The only drawback is that Andi's idea of idle=mwait wouldn't make
> sense anymore.

Well, if there is use for the AMD implementation of monitor/mwait, then 
that's a different situation, and probably would call for multiple 
feature bits.

	-hpa
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