Messages in this thread | | | Date | Wed, 16 Mar 2022 17:23:31 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH v4] arch/x86: Improve 'rep movs{b|q}' usage in memmove_64.S |
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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
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