linux-kernel - Re: [PATCH] x86: Add clflush before monitor for Intel 7400 series

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Date:	Sat, 18 Oct 2008 09:15:39 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: Add clflush before monitor for Intel 7400 series

"H. Peter Anvin" <hpa@...or.com> writes:

> Pallipadi, Venkatesh wrote:
>>>>
>>> I guess I'm a bit confused about the tradeoff of CLFLUSH versus simply
>>> disabling MWAIT.  This is a relatively recent processor and so
>>> optimizing matters (if this was a P4 I would be more worried about what
>>> has least impact on the kernel as a whole.)
>> As of now this is only for a limited models of CPUs (MP CPUs)
>> and not a norm. It is a errata on this CPU and not
>> something that is going to become architectural.
>>
>
> Yes, I understand.  However, there is still the option to disable
> MWAIT, and the question is still open if it makes sense.

This would mean falling back to the IO port interface for deeper 
C states. Even with the CLFLUSH MWAIT is a much better (and I believe 
faster) interface.

-Andi
-- 
ak@...ux.intel.com
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