Re: [PATCH] Performance optimization for detection of modified submodules

From: Junio C Hamano <gitster@pobox.com>
Date: Jan 17, 2010, 20:01 UTC
Message-ID: <7vska4xzzf.fsf@alter.siamese.dyndns.org>
In-Reply-To: <4B535E97.1020809@web.de>

Jens Lehmann <Jens.Lehmann@web.de> writes:

Show 6 quoted lines

> So here is my first attempt of implementing your proposal. The test suite
> runs fine, but a few more eyeballs would really be appreciated as i am not
> very familiar with the code and its corner cases (See diff_change(), is it
> sufficient to only set "two->dirty_submodule", even if the REVERSE_DIFF
> option is set? Apart from that i am not so sure about the four changes to
> tree-diff.c).

The effect of REVERSE_DIFF bit is contained in the output layer. The order frontends (e.g. diff-files and diff-lib.c::run_diff_files()) feed the entries from two hierarchies is not affected.

The current callers of addremove() may always give the work tree side as the second one, but the API is meant to be usable by any other new callers and for some of them feeding the work tree side as the first one _might_ be more sensible (we are talking about futureproofing, so by definition we won't know). It might even be the case where an unanticipated new caller might be comparing two trees both living in the work tree (hence you might require two independent dirty_submodule bits to the call to show which side is dirty, and such a caller may say "both sides are dirty").

So it would be most future-proof if you add two independent "dirty" bits to the API if you are changing it: "is the left side of the comparision a dirty submodule?" and "is the right side ...?". Especially I don't think assuming "setting two->dirty is enough for the current implementation" is the right way going forward.

> I think we could skip the call to is_submodule_modified() in
> run_diff_files() and get_stat_data() when the changed flag is already
> set and only short output (without calling diff_populate_gitlink(), e.g.
> "git status -s" or "git diff-files") is requested.

I am puzzled by your "we could skip"; isn't it what you already have done in this patch? More importantly, I think that is the whole point of the change to diff API this patch brings in.

> What do you think
> about doing that in a seperate patch?

Doing these in this same patch like you did is better, as it demonstrates how the callers benefit by the addition of these new bits to the API.