Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH v4] arch/x86: Improve 'rep movs{b|q}' usage in memmove_64.S | Date | Wed, 17 Nov 2021 22:31:21 +0000 |
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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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