threads / discuss / 9811

very slow cherry-pick'ing (old-2.6-bkcvs tree)

Subject: very slow cherry-pick'ing (old-2.6-bkcvs tree)

## tl;dr

3 messages between Sep 6, 2007 and Sep 7, 2007.

replies: 2people: 3as markdown or json

Erez Zadok· Sep 6, 2007, 23:51 UTC · lore

Our group maintains Unionfs on the latest -rc kernel, but we also maintain several backports going all the way to 2.6.9. Once we complete the development and testing of a feature/fix in -latest, we cherry-pick those commits to older backports, and test those. When I cherry-pick from -latest to my 2.6.{22,21,20,19,18} repositories, it works reasonably fast. But when I cherry-pick to my 2.6.9 tree, it runs about 20 times slower! Why? Is there anything I can do to inspect what's going on and perhaps speed up the cherry-picking process?

Some info:

My 2.6.{18,19,20,21,22} trees were cloned from

   git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-2.6.<N>.y.git

My 2.6.9 tree, however, was cloned from

   git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/old-2.6-bkcvs.git

after which, I truncated the tree (git-reset) to Linus commit which read "Linux 2.6.9-final".

BTW, I first git-clone --bare to my git server, and then I clone from it to my test machine.

BTW2, I do git-repack and prune-packed every week.

Thanks, Erez.

Shawn O. Pearce· Sep 7, 2007, 04:42 UTC · re: Erez Zadok · lore

Re: very slow cherry-pick'ing (old-2.6-bkcvs tree)

Erez Zadok <ezk@cs.sunysb.edu> wrote:

Show 8 quoted lines

> Our group maintains Unionfs on the latest -rc kernel, but we also maintain
> several backports going all the way to 2.6.9.  Once we complete the
> development and testing of a feature/fix in -latest, we cherry-pick those
> commits to older backports, and test those.  When I cherry-pick from -latest
> to my 2.6.{22,21,20,19,18} repositories, it works reasonably fast.  But when
> I cherry-pick to my 2.6.9 tree, it runs about 20 times slower!  Why?  Is
> there anything I can do to inspect what's going on and perhaps speed up the
> cherry-picking process?

I'm guessing its due to rename detection.

git-cherry-pick is implemented in terms of git-merge-recursive, which always does rename detection when files are deleted or added. This can take some considerable time if there's a lot of files that have been added/deleted.

What would probably be faster would be to dump the patches in question using git-format-patch and then apply them using git-am. This bypasses the rename detection as it is using strictly a diff and an apply.

-- 
Shawn.

Johannes Sixt· Sep 7, 2007, 07:27 UTC · re: Erez Zadok · lore

Re: very slow cherry-pick'ing (old-2.6-bkcvs tree)

Erez Zadok schrieb:

Show 21 quoted lines

> Our group maintains Unionfs on the latest -rc kernel, but we also maintain
> several backports going all the way to 2.6.9.  Once we complete the
> development and testing of a feature/fix in -latest, we cherry-pick those
> commits to older backports, and test those.  When I cherry-pick from -latest
> to my 2.6.{22,21,20,19,18} repositories, it works reasonably fast.  But when
> I cherry-pick to my 2.6.9 tree, it runs about 20 times slower!  Why?  Is
> there anything I can do to inspect what's going on and perhaps speed up the
> cherry-picking process?
> 
> Some info:
> 
> My 2.6.{18,19,20,21,22} trees were cloned from
> 
>    git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-2.6.<N>.y.git
> 
> My 2.6.9 tree, however, was cloned from
> 
>    git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/old-2.6-bkcvs.git
> 
> after which, I truncated the tree (git-reset) to Linus commit which read
> "Linux 2.6.9-final".

I *think* that the reason for this is that those repositories don't have any commits in common (but I don't have clones to verify my claim). Since cherry-pick does merge-recursive, it tries to find a suitable merge base, but since there is no history in common, it walks both histories all the way down only to find that there is no possible merge base.

You could improve the situation if you graft the histories together:

   echo $first_commit_in_2.6.12 $suitable_commit_in_bkcvs > .git/info/grafts

-- Hannes