linux-kernel - Re: [PATCH 4/8] x86/asm: add clear_page

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Message-ID: <20201014195614.GB18196@zn.tnic>
Date:   Wed, 14 Oct 2020 21:56:14 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Ankur Arora <ankur.a.arora@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kirill@...temov.name, mhocko@...nel.org,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Jiri Slaby <jslaby@...e.cz>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH 4/8] x86/asm: add clear_page_nt()

On Wed, Oct 14, 2020 at 01:32:55AM -0700, Ankur Arora wrote:
> This can potentially improve page-clearing bandwidth (see below for
> performance numbers for two microarchitectures where it helps and one
> where it doesn't) and can help indirectly by consuming less cache
> resources.
> 
> Any performance benefits are expected for extents larger than LLC-sized
> or more -- when we are DRAM-BW constrained rather than cache-BW
> constrained.

"potentially", "expected", I don't like those formulations. Do you have
some actual benchmark data where this shows any improvement and not
microbenchmarks only, to warrant the additional complexity?

-- 
Regards/Gruss,
    Boris.

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