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SubjectRe: [PATCH 207/208] x86/fpu: Add FPU performance measurement subsystem

* Dave Hansen <dave.hansen@linux.intel.com> wrote:

> On 05/05/2015 10:58 AM, Ingo Molnar wrote:
> > x86/fpu: Cost of: XSAVE insn : 104 cycles
> > x86/fpu: Cost of: XRSTOR insn : 80 cycles
>
> Isn't there going to be pretty huge variability here depending on
> how much state you are xsave/xrstor'ing and if the init/modified
> optimizations are in play?

Hopefully there's such variability! :)

I thought to add measurements for that as well:

- to see the costs of this instruction family when various xstate
components are in 'init state' or not

- maybe even measure whether it can optimize based on whether things
got changed since the last save (which the SDM kind of alludes to
but which I doubt the hw does)?

This initial version only measures trivial init state save/restore
cost.

Thanks,

Ingo


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