[PATCH 0/3] Un-pessimize "diff-index $commit -- $pathspec"

[Junio C Hamano <gitster@pobox.com>]

"git diff A B -- $pathspec" to compare two tree-ishes knew how to apply
pathspec to avoid opening trees that fall outside the area of interest,
but "git diff A -- $pathspec" used unpack_trees() machinery that was meant
for full-tree merges, and ended up reading the whole tree only to discard
potentially major part of the work it does.

Before and after applying this series, looking for changes in the kernel
repository with a fairly narrow pathspec gets a moderate speeds up.

  (without patch)
  $ /usr/bin/time git diff --raw v2.6.27 -- net/ipv6 >/dev/null
  0.48user 0.05system 0:00.53elapsed 100%CPU (0avgtext+0avgdata 163296maxresident)k
  0inputs+952outputs (0major+11163minor)pagefaults 0swaps

  (with patch)
  $ /usr/bin/time git diff --raw v2.6.27 -- net/ipv6 >/dev/null
  0.01user 0.00system 0:00.02elapsed 104%CPU (0avgtext+0avgdata 43856maxresident)k
  0inputs+24outputs (0major+3688minor)pagefaults 0swaps

Junio C Hamano (3):
  tree-walk: allow pruning with pathspec
  unpack-trees: allow pruning with pathspec
  diff-index: pass pathspec down to unpack-trees machinery

 diff-lib.c     |    1 +
 tree-walk.c    |   39 +++++++++++++++++++++++++++++++++------
 tree-walk.h    |    1 +
 unpack-trees.c |    2 ++
 unpack-trees.h |    1 +
 5 files changed, 38 insertions(+), 6 deletions(-)

-- 
1.7.7.rc0.70.g82660