Derrick Stolee <dstolee@xxxxxxxxxxxxx> writes:
> The containment algorithm for 'git branch --contains' is different
> from that for 'git tag --contains' in that it uses is_descendant_of()
> instead of contains_tag_algo(). The expensive portion of the branch
> algorithm is computing merge bases.
>
> When a commit-graph file exists with generation numbers computed,
> we can avoid this merge-base calculation when the target commit has
> a larger generation number than the initial commits.
Right.
>
> Performance tests were run on a copy of the Linux repository where
> HEAD is contained in v4.13 but no earlier tag. Also, all tags were
> copied to branches and 'git branch --contains' was tested:
I guess that it is equivalent of 'git tag --contains' setup from
previous commit, just for 'git branch --contains', isn't it?
>
> Before: 60.0s
> After: 0.4s
> Rel %: -99.3%
Very nice.
Sidenote: an alternative to using "Rel %" of -99.3% (which is calculated
as (before-after)/before) would be to use "Speedup" of 150 x (calculated
as before/after). One one hand it might be more readable, on the other
hand it might be a bit misleading.
Yet another alternative would be to use a chart like the following:
time Before After
Before 60.0s -- -99.3%
After 0.4s +149% --
Anyway, consistency in presentation in patch series is good. So I am
for keeping your notation thorough the series.
>
> Reported-by: Jeff King <peff@xxxxxxxx>
> Signed-off-by: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
> ---
> commit.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/commit.c b/commit.c
> index 39a3749abd..7bb007f56a 100644
> --- a/commit.c
> +++ b/commit.c
> @@ -1056,12 +1056,19 @@ int in_merge_bases_many(struct commit *commit, int nr_reference, struct commit *
Let's give it a bit more context:
/*
* Is "commit" an ancestor of one of the "references"?
*/
int in_merge_bases_many(struct commit *commit, int nr_reference, struct commit **reference)
> {
> struct commit_list *bases;
> int ret = 0, i;
> + uint32_t min_generation = GENERATION_NUMBER_INFINITY;
>
> if (parse_commit(commit))
> return ret;
> - for (i = 0; i < nr_reference; i++)
> + for (i = 0; i < nr_reference; i++) {
> if (parse_commit(reference[i]))
> return ret;
We use parse_commit(), so there is no need for calling
load_commit_graph_info(), like in previous patch.
All right.
> + if (min_generation > reference[i]->generation)
At first glance, I thought it was wrong; but it is the same as the
following, it is just a matter of taste (which feels more natural):
+ if (reference[i]->generation < min_generation)
> + min_generation = reference[i]->generation;
> + }
> +
> + if (commit->generation > min_generation)
> + return ret;
All right, using weak version of generation numbers based negative-cut
nicely handles automatically all corner-cases, including the case where
commit-graaph feature is turned off.
If commit-graph feature is not available, it costs only few memory
access and few comparisons than before, and performance is dominated by
something else anyway. Negligible and possibly unnoticeable change, I
guess. Good.
>
> bases = paint_down_to_common(commit, nr_reference, reference);
> if (commit->object.flags & PARENT2)
