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From: Borislav Petkov <[email protected]>
To: Noah Goldstein <[email protected]>
Cc: [email protected], [email protected], [email protected],
	[email protected], [email protected], [email protected]
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: <[email protected]> (raw)
In-Reply-To: <[email protected]>

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: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <[email protected]>
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     [not found]       ` <[email protected]>
     [not found]         ` <CAFUsyfLUQLj5py1AQ+4NptM6htWxV5i0qxkeXDUdFPfAnqRY2w@mail.gmail.com>
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     [not found]               ` <CAFUsyf+4vgZsM9gdyN1=eP_MzDsuOXOdKitS=1Rj-jBpdFGg9Q@mail.gmail.com>
2022-03-16 14:15                 ` [PATCH v4] arch/x86: Improve 'rep movs{b|q}' usage in memmove_64.S Noah Goldstein
2022-03-16 16:23   ` Borislav Petkov [this message]

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