Messages in this thread |  | | | Date | Wed, 30 Mar 2011 11:15:38 -0500 (CDT) | | From | Christoph Lameter <> | | Subject | Re: [PATCH tip:x86/mm 1/3] x86: A fast way to check capabilities of the current cpu |
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On Wed, 30 Mar 2011, Tejun Heo wrote:
> Hello, > > On Wed, Mar 30, 2011 at 08:58:23AM -0700, H. Peter Anvin wrote: > > >> 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()). > > These patches have performance benefits but I don't think it would be > noticeable. I think it's more of code cleanup.
The main simplification is that the pointer to the cpu_info can be omitted. Its passed around quite a bit right now in x86 arch code. Removal of the cpu_info pointer could reduce code size and allow faster access.
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