Messages in this thread | | | Date | Tue, 5 Apr 2016 17:11:56 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH 1/6] x86/fpu/regset: Use boot_cpu_has() |
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On Tue, Apr 05, 2016 at 09:51:55AM -0400, Brian Gerst wrote: > I think the general rule should be always use static_cpu_has() for > runtime checks, since it reduces down to a single jmp/nop instruction > after alternatives run. Even if it's not a hot path, it saves a bit > of runtime memory.
So gcc generates a MOV and a TEST for boot_cpu_has(). Not exactly the bloat or slowdown.
So I look at those differently: static_cpu_has()
a) should be used on hotpaths
b) is used as such to annotate those - i.e., "ah, there's a static_cpu_has(), this is a hot path, I better be careful what I'm doing here."
boot_cpu_has() in all the rest.
And saving a couple of bytes per call site but increasing alternatives application time by milli- or microseconds... Meh. I don't see it being really worth the trouble. But this is just me.
-- Regards/Gruss, Boris.
ECO tip #101: Trim your mails when you reply.
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