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    • Linus Torvalds's avatar
      x86/csum: clean up `csum_partial' further · a476aae3
      Linus Torvalds authored
      Commit 688eb819 ("x86/csum: Improve performance of `csum_partial`")
      ended up improving the code generation for the IP csum calculations, and
      in particular special-casing the 40-byte case that is a hot case for
      IPv6 headers.
      
      It then had _another_ special case for the 64-byte unrolled loop, which
      did two chains of 32-byte blocks, which allows modern CPU's to improve
      performance by doing the chains in parallel thanks to renaming the carry
      flag.
      
      This just unifies the special cases and combines them into just one
      single helper the 40-byte csum case, and replaces the 64-byte case by a
      80-byte case that just does that single helper twice.  It avoids having
      all these different versions of inline assembly, and actually improved
      performance further in my tests.
      
      There was never anything magical about the 64-byte unrolled case, even
      though it happens to be a common size (and typically is the cacheline
      size).
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      a476aae3