RE: [PATCH v4] arch/x86: Improve 'rep movs{b|q}' usage in memmove_64.S

[David Laight]

From: Noah Goldstein
> Sent: 17 November 2021 21:03
> 
> 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.

How does this relate to the decision that glibc made a few years
ago to use backwards 'rep movs' for non-overlapping copies?

Did they find a different corner case??

	David

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