linux-kernel - Re: [PATCH] x86: make clflush a required feature on x86

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Date:	Fri, 18 Jan 2008 15:18:39 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andi Kleen <andi@...stfloor.org>, Kyle McMartin <kyle@...artin.ca>,
	tglx@...utronix.de, mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: make clflush a required feature on x86_64

On Fri, Jan 18, 2008 at 08:56:43AM -0500, H. Peter Anvin wrote:
> Andi Kleen wrote:
> >>Simulators can be fixed, 
> >
> >They could, but why? I don't know of a good reason to require CLFLUSH.
> 
> Well, simulators are generally expected to follow the architecture, not 
> vice versa.  I would tend to agree with the coupling that recent 
> versions of Bochs appeared to have made here -- I think we're unlikely 
> to see any processors with sse2 sans clflush, so keeping code branches 
> in which will never be executed seems like a bad idea in the long term. 

Here's another argument: Ingo just asked me to add a noclflush option
to the code. Guess what check that option will need? 

Besides compared to the cost of a flushing clflush the branches are absolutely 
in the noise.

-Andi
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