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[Bug string/19928] New: memmove-vec-unaligned-erms.S is slow with large data size


https://sourceware.org/bugzilla/show_bug.cgi?id=19928

            Bug ID: 19928
           Summary: memmove-vec-unaligned-erms.S is slow with large data
                    size
           Product: glibc
           Version: 2.24
            Status: NEW
          Severity: normal
          Priority: P2
         Component: string
          Assignee: unassigned at sourceware dot org
          Reporter: hjl.tools at gmail dot com
  Target Milestone: ---
            Target: x86-64

Created attachment 9171
  --> https://sourceware.org/bugzilla/attachment.cgi?id=9171&action=edit
bench-memcpy data on Intel Haswell machine with large data size

The large memcpy micro benchmark in glibc shows that there is a regression
with large data on Haswell.  memmove-vec-unaligned-erms.S doesn't use
non-temporal store with large data size.  Benchmark data shows that the
threshold to use non temporal store is approximately 6 times of shared cache
size.  But non temporal store isn't a win on large data size when there is
overlap between destination and source since destination may be in cache
when source is loaded.

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