Re: [PATCH] perf: optimize clear page in Intel specified model with movq instruction

[Luming Yu]

On Thu, Sep 9, 2021 at 5:41 PM Borislav Petkov <bp@xxxxxxxxx> wrote:
>
> On Thu, Sep 09, 2021 at 04:45:51PM +0800, Jinhua Wu wrote:
> > Clear page is the most time-consuming procedure in page fault handling.
> > Kernel use fast-string instruction to clear page. We found that in specified
> > Intel model such as CPX and ICX, the movq instruction perform much better
> > than fast-string instruction when corresponding page is not in cache.
> > But when the page is in cache, fast string perform better. We show the test
> > result in the following:
>
> What you should do is show the extensive tests you've run with
> real-world benchmarks where you really can show 40% performance
> improvement.
>
> Also, the static branch "approach" you're using ain't gonna happen. If
> anything, another X86_FEATURE_* bit.

do you mean jump label would not be replaced to nop when its key is enabled?
so we could not use it in certain functions?
I don't understand exactly what "ain't  gonna happen"
>
> Good luck.
>
> --
> Regards/Gruss,
>     Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette