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

From: Andi Kleen
Date: Sat Oct 18 2008 - 03:15:54 EST

"H. Peter Anvin" <hpa@xxxxxxxxx> 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.

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