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From: Borislav Petkov <bp@alien8.de>
To: Noah Goldstein <goldstein.w.n@gmail.com>
Cc: tglx@linutronix.de, mingo@redhat.com, x86@kernel.org,
	hpa@zytor.com, luto@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] arch/x86: Improve 'rep movs{b|q}' usage in memmove_64.S
Date: Wed, 16 Mar 2022 17:23:31 +0100	[thread overview]
Message-ID: <YjIPA1IagZDdi7iw@zn.tnic> (raw)
In-Reply-To: <20211117210245.843374-1-goldstein.w.n@gmail.com>

On Wed, Nov 17, 2021 at 03:02:45PM -0600, Noah Goldstein wrote:
> Add check for "short distance movsb" for forwards FSRM usage and
> entirely remove backwards 'rep movsq'. Both of these usages hit "slow
> modes" that are an order of magnitude slower than usual.
> 
> 'rep movsb' has some noticeable VERY slow modes that the current
> implementation is either 1) not checking for or 2) intentionally
> using.
> 
> All times are in cycles and measuring the throughput of copying 1024
> bytes.

All these claims need to be proven by

 - real benchmarks - not a microbenchmark - where it shows that
 modifications like that are not "in the noise". Others should be able
 to verify those results too.

 - on a bunch of CPUs from different vendors to verify that they don't
   cause performance regressions on any.

HTH.

-- 
Regards/Gruss,
    Boris.

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

      parent reply	other threads:[~2022-03-16 16:23 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-01  4:49 [PATCH v1] " Noah Goldstein
2021-11-01 18:59 ` [PATCH v2] " Noah Goldstein
2021-11-02 23:15 ` [PATCH v3] " Noah Goldstein
2021-11-17 21:02 ` [PATCH v4] " Noah Goldstein
2021-11-17 22:31   ` David Laight
2021-11-17 22:45     ` Noah Goldstein
2021-11-19 22:31       ` David Laight
2021-11-20  0:05         ` Noah Goldstein
2021-12-10 18:35           ` Noah Goldstein
2022-01-12  3:13             ` Noah Goldstein
2022-02-10  9:08               ` Noah Goldstein
2022-03-16 14:15                 ` Noah Goldstein
2022-03-16 16:23   ` Borislav Petkov [this message]

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