Messages in this thread | | | Date | Wed, 30 Mar 2011 09:16:52 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH tip:x86/mm 1/3] x86: A fast way to check capabilities of the current cpu |
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On 03/30/2011 08:58 AM, H. Peter Anvin wrote: > On 03/14/2011 12:49 PM, Andi Kleen wrote: >> Tejun Heo <tj@kernel.org> writes: >> >>> Add this_cpu_has() which determines if the current cpu has a certain >>> ability using a segment prefix and a bit test operation. >> >> >> Hmm: if the CPU capability is really tested in a performance critical >> path, wouldn't it even be better to just use static_branch() now? >> > > We have static_cpu_has() for this specific purpose (it actually predates > static_branch()). >
Note that static_cpu_has() has two caveats:
1. Before alternatives patching, it will always be false. 2. It is the equivalent of boot_cpu_has(), i.e. the intersection of all the CPU feature sets (available at boot time, obviously.)
-hpa
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