On Mon, Jul 30, 2018 at 8:10 PM Ben Peart <peartben@xxxxxxxxx> wrote: > I ran "git checkout" on a large repo and averaged the results of 3 runs. > This clearly demonstrates the benefit of the optimized unpack_trees() > as even the final "diff-index" is essentially a 3rd call to unpack_trees(). > > baseline new > ---------------------------------------------------------------------- > 0.535510167 0.556558733 s: read cache .git/index > 0.3057373 0.3147105 s: initialize name hash > 0.0184082 0.023558433 s: preload index > 0.086910967 0.089085967 s: refresh index > 7.889590767 2.191554433 s: unpack trees > 0.120760833 0.131941267 s: update worktree after a merge > 2.2583504 2.572663167 s: repair cache-tree > 0.8916137 0.959495233 s: write index, changed mask = 28 > 3.405199233 0.2710663 s: unpack trees > 0.000999667 0.0021554 s: update worktree after a merge > 3.4063306 0.273318333 s: diff-index > 16.9524923 9.462943133 s: git command: > 'c:\git-sdk-64\usr\src\git\git.exe' checkout > > The first call to unpack_trees() saves 72% > The 2nd and 3rd call save 92% By the 3rd I guess you meant "diff-index" line. I think it's the same with the second call. diff-index triggers the second unpack-trees but there's no indent here and it's misleading to read this as diff-index and unpack-trees execute one after the other. > Total time savings for the entire command was 44% Wow.. I guess you have more trees since I could only save 30% on gcc.git. > In the performance game of whack-a-mole, that call to repair cache-tree > is now looking quite expensive... Yeah and I think we can whack that mole too. I did some measurement. Best case possible, we just need to scan through two indexes (one with many good cache-tree, one with no cache-tree), compare and copy cache-tree over. The scanning takes like 1% time of current repair step and I suspect it's the hashing that takes most of the time. Of course real world won't have such nice numbers, but I guess we could maybe half cache-tree update/repair time. -- Duy
