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

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Date:   Thu, 9 Sep 2021 11:39:40 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Jinhua Wu <wujinhua@...ux.alibaba.com>
Cc:     x86@...nel.org, zelin.deng@...ux.alibaba.com,
        jiayu.ni@...ux.alibaba.com, ak@...ux.intel.com,
        luming.yu@...el.com, fan.du@...el.com,
        artie.ding@...ux.alibaba.com, tony.luck@...el.com,
        tglx@...utronix.de, linux-kernel@...r.kernel.org,
        pawan.kumar.gupta@...ux.intel.com, fenghua.yu@...el.com,
        hpa@...or.com, ricardo.neri-calderon@...ux.intel.com,
        peterz@...radead.org
Subject: Re: [PATCH] perf: optimize clear page in Intel specified model with
 movq instruction

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.

Good luck.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette