Re: [lkp] [x86/hweight] 65ea11ec6a: will-it-scale.per_process_ops 9.3% improvement

[Borislav Petkov]

On Tue, Aug 16, 2016 at 04:09:19PM -0700, H. Peter Anvin wrote:
> On August 16, 2016 10:16:35 AM PDT, Borislav Petkov <bp@xxxxxxx> wrote:
> >On Tue, Aug 16, 2016 at 09:59:00AM -0700, H. Peter Anvin wrote:
> >> Dang...
> >
> >Isn't 9.3% improvement a good thing(tm) ?
> 
> Yes, it's huge.  The only explanation I could imagine is that scrambling %rdi caused the scheduler to do completely the wrong thing.

I'm questioning the validity, actually. Report says test machine was
Sandy Bridge-EP and I'd bet good money this one has POPCNT support so
how are we even hitting that __sw_hweight64() path, at all?

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