Messages in this thread | | | Date | Sun, 31 Mar 2019 17:12:48 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH 3/5] x86/kvm: Convert some slow-path static_cpu_has() callers to boot_cpu_has() |
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On Sun, Mar 31, 2019 at 04:20:11PM +0200, Paolo Bonzini wrote: > These are not slow path.
Those functions do a *lot* of stuff like a bunch of MSR reads which are tens of cycles each at least.
I don't think a RIP-relative MOV and a BT:
movq boot_cpu_data+20(%rip), %rax # MEM[(const long unsigned int *)&boot_cpu_data + 20B], _45 btq $59, %rax #, _45
are at all noticeable.
On latest AMD and Intel uarch those are 2-4 cycles, according to
https://agner.org/optimize/instruction_tables.ods
-- Regards/Gruss, Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
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