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.
