On Mon, Feb 24, 2014 at 11:21 PM, Kirill Smelkov <k...@mns.spb.ru> wrote:
> Hello up there.
> Here go combine-diff speedup patches in form of first reworking diff
> tree-walker to work in general case - when a commit have several parents, not
> only one - we are traversing all 1+nparent trees in parallel.
> Then we are taking advantage of the new diff tree-walker for speeding up
> combine-diff, which for linux.git results in ~14 times speedup.

I think there is another use case for this n-tree walker (but I'm not
entirely sure yet as I haven't really read the series). In git-log
(either with pathspec or --patch) we basically do this

diff HEAD^^ HEAD^
diff HEAD^^^ HEAD^^
diff HEAD^^^^ HEAD^^^

so except HEAD (and the last commit), all commits' tree will be
read/diff'd twice. With n-tree walker I think we may be able to diff
them in batch to reduce extra processing: commit lists are split into
16-commit blocks where 16 trees are fed to the new tree walker at the
same time. I hope it would make git-log a bit faster (especially for
-S). Maybe not much.
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