Messages in this thread | | | Date | Thu, 13 Nov 2008 17:20:08 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes |
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Nick Piggin wrote: > > I heard from an Intel hardware engineer that Nehalem has some > really fancy logic in it to make locked instructions "free", that > was nacked from earlier CPUs because it was too costly. So obviously > it is taking a fair whack of transistors or power for them to do it. > And even then it is far from free, but still seems to be one or two > orders of magnitude more expensive than a regular instruction. >
Last I heard it was still a dozen-ish cycles even on Nehalem.
> > IMO, we shouldn't stop bothering about LOCK prefix in the forseeable > future. >
Even if a CPU came out *today* that had zero-cost locks we'd have to worry about it for at least another 5-10 years. The good news is that we're doing pretty good with it for now, but I don't believe in general we can avoid the fact that improving LOCK performance helps everything when you're dealing with large numbers of cores/threads.
-hpa
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