Re: [RFC/PATCH 0/2] Enhance performance of blame -C -C

Alexander Gavrilov [off-list ref] writes:

This pair of patches aims at increasing performance of copy detection in
blame by avoiding unnecessary comparisons. Note that since I'm new to
this code, I might have misunderstood something.

There are two cases than I aim to fix:

1) Copy detection is done by comparing all outstanding chunks of the
target file to all blobs in the parent. After that, chunks with suitable
matches are split, and comparison is repeated again, until there are no
new matches. The trouble is, chunks that didn't match the first time,
and weren't split, are compared against the same set of blobs again and
again. I add a flag to track that.

  On my test case it decreased blame -C -C time from over 10min to
  ~6min; 4min with -C80.

2) Chunks are split only if the match scores above a certain
threshold. I understand that a split of an entry cannot score more than
the entry itself. Thus, it is pointless to even try doing costly
comparisons for small entries.

  (Time goes down to 4min; 2min with -C80)

Ideas for both patches sound very sane.  Will take a deeper look later.

Thanks.