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Message-ID: <4F16F505.8040809@zytor.com> Date: Wed, 18 Jan 2012 08:36:21 -0800 From: "H. Peter Anvin" <hpa@...or.com> To: Jan Beulich <JBeulich@...e.com> CC: mingo@...e.hu, tglx@...utronix.de, "eric.dumazet@...il.com" <eric.dumazet@...il.com>, luca@...a-barbieri.com, linux-kernel@...r.kernel.org Subject: Re: [PATCH 2/2] ix86: atomic64 assembly improvements On 01/18/2012 06:24 AM, Jan Beulich wrote: > The cmpxchg8b variants of "set" and "xchg" are really identical, and > hence don't need to be repeated: %ebx and %ecx don't need to be copied > into %eax and %edx respectively (this is only necessary when desiring > to only read the stored value), and the LOCK prefix should also be used > in "set" (other than the comment that is now being removed was saying, > there is - to my knowledge - no *architectural* guarantee that aligned > 64-bit writes would always be carried out atomically). EWHAT? It's atomic in the same way a MOV is atomic. The CPU could, in fact, execute the locked version at all if the unlocked version didn't behave like that. Unless you have a specific instance where you think this might be violated, please let me know. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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