linux-kernel - Re: P6 NOPs again: MPSC?

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Date:	Tue, 11 Mar 2008 07:43:25 +0100
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Hugh Dickins <hugh@...itas.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: P6 NOPs again: MPSC?

Hugh Dickins wrote:
> 
> Yup, I realized that (with || in place of &&): I meant that perhaps
> it was supposed to say X86_64 || (!X86_GENERIC && (M686 || ....))
> since quite a lot of other options there have "|| X86_64" to cover
> all the 64-bit possibilities at once i.e. is it only MPSC that
> needs to be added, or both MPSC and CPU_GENERIC?
> 

No.  The left-hand clause (X86_64 || !X86_GENERIC) indicates when using 
these NOPs are *permitted*; the right-hand clause indicates when doing 
so is *desirable*.  The latter isn't, for example, for K8, even on 64 bits.

	-hpa

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