This patch series performs a decently-sized refactoring of the
revision-walk machinery. Well, "refactoring" is probably the wrong word,
as I don't actually remove the old code. Instead, when we see certain
options in the 'rev_info' struct, we redirect the commit-walk logic to
a new set of methods that distribute the workload differently. By using
generation numbers in the commit-graph, we can significantly improve
'git log --graph' commands (and the underlying 'git rev-list --topo-order').
On the Linux repository, I got the following performance results when
comparing to the previous version with or without a commit-graph:
Test: git rev-list --topo-order -100 HEAD
HEAD~1, no commit-graph: 6.80 s
HEAD~1, w/ commit-graph: 0.77 s
HEAD, w/ commit-graph: 0.02 s
Test: git rev-list --topo-order -100 HEAD -- tools
HEAD~1, no commit-graph: 9.63 s
HEAD~1, w/ commit-graph: 6.06 s
HEAD, w/ commit-graph: 0.06 s
If you want to read this series but are unfamiliar with the commit-graph
and generation numbers, then I recommend reading
`Documentation/technical/commit-graph.txt` or a blog post [1] I wrote on
the subject. In particular, the three-part walk described in "revision.c:
refactor basic topo-order logic" is present (but underexplained) as an
animated PNG [2].
**UPDATED** Now that we have had some review and some dogfooding, I'm
removing the paragraph I had here about "RFC quality". I think this is
ready to merge!
One notable case that is not included in this series is the case of a
history comparison such as 'git rev-list --topo-order A..B'. The existing
code in limit_list() has ways to cut the walk short when all pending
commits are UNINTERESTING. Since this code depends on commit_list instead
of the prio_queue we are using here, I chose to leave it untouched for now.
We can revisit it in a separate series later. Since handle_commit() turns
on revs->limited when a commit is UNINTERESTING, we do not hit the new
code in this case. Removing this 'revs->limited = 1;' line yields correct
results, but the performance can be worse.
**UPDATED** See the discussion about Generation Number V2 [4] for more
on this topic.
Changes in V5: Thanks Jakub for feedback on the huge commit! I think
I've responded to all the code feedback. See the range-diff at the
end of this cover-page.
Thanks,
-Stolee
[1] https://blogs.msdn.microsoft.com/devops/2018/07/09/supercharging-the-git-commit-graph-iii-generations/
Supercharging the Git Commit Graph III: Generations and Graph Algorithms
[2] https://msdnshared.blob.core.windows.net/media/2018/06/commit-graph-topo-order-b-a.png
Animation showing three-part walk
[3] https://github.com/derrickstolee/git/tree/topo-order/test
A branch containing this series along with commits to compute commit-graph in entire test suite.
[4] https://public-inbox.org/git/6367e30a-1b3a-4fe9-611b-d931f51effef@xxxxxxxxx/
[RFC] Generation Number v2
Note: I'm not submitting this version via GitGitGadget because it's
currently struggling with how to handle a PR in a conflict state.
The new flags in revision.h have a conflict with recent changes in
master.
Derrick Stolee (7):
prio-queue: add 'peek' operation
test-reach: add run_three_modes method
test-reach: add rev-list tests
revision.c: begin refactoring --topo-order logic
commit/revisions: bookkeeping before refactoring
revision.c: generation-based topo-order algorithm
t6012: make rev-list tests more interesting
commit.c | 9 +-
commit.h | 7 +
object.h | 4 +-
prio-queue.c | 9 ++
prio-queue.h | 6 +
revision.c | 243 +++++++++++++++++++++++++++++++++--
revision.h | 6 +
t/helper/test-prio-queue.c | 26 ++--
t/t0009-prio-queue.sh | 14 ++
t/t6012-rev-list-simplify.sh | 45 +++++--
t/t6600-test-reach.sh | 96 +++++++++++++-
11 files changed, 426 insertions(+), 39 deletions(-)
base-commit: 2d3b1c576c85b7f5db1f418907af00ab88e0c303
--
2.19.1.542.gc4df23f792
-->8--
1: 2358cfd5ed = 1: 7c75a56505 prio-queue: add 'peek' operation
2: 3a4b68e479 = 2: 686c4370de test-reach: add run_three_modes method
3: 12a3f6d367 = 3: 7410c00982 test-reach: add rev-list tests
4: cd9eef9688 = 4: 5439e11e37 revision.c: begin refactoring --topo-order logic
5: f3e291665d ! 5: 71554deb9b commit/revisions: bookkeeping before refactoring
@@ -9,8 +9,8 @@
compare_commits_by_author_date() in revision.c. These are used
currently by sort_in_topological_order() in commit.c.
- 2. Moving these methods to commit.h requires adding the author_slab
- definition to commit.h.
+ 2. Moving these methods to commit.h requires adding an author_date_slab
+ declaration to commit.h. Consumers will need their own implementation.
3. The add_parents_to_list() method in revision.c performs logic
around the UNINTERESTING flag and other special cases depending
@@ -31,8 +31,7 @@
define_commit_slab(indegree_slab, int);
-/* record author-date for each commit object */
--define_commit_slab(author_date_slab, timestamp_t);
-+implement_shared_commit_slab(author_date_slab, timestamp_t);
+ define_commit_slab(author_date_slab, timestamp_t);
-static void record_author_date(struct author_date_slab *author_date,
- struct commit *commit)
@@ -69,8 +68,7 @@
extern int check_commit_signature(const struct commit *commit, struct signature_check *sigc);
+/* record author-date for each commit object */
-+define_shared_commit_slab(author_date_slab, timestamp_t);
-+
++struct author_date_slab;
+void record_author_date(struct author_date_slab *author_date,
+ struct commit *commit);
+
6: aa0bb2221d ! 6: 84c142e0bc revision.c: generation-based topo-order algorithm
@@ -195,6 +195,7 @@
-struct topo_walk_info {};
+define_commit_slab(indegree_slab, int);
++define_commit_slab(author_date_slab, timestamp_t);
+
+struct topo_walk_info {
+ uint32_t min_generation;
@@ -243,12 +244,12 @@
+}
+
+static void explore_to_depth(struct rev_info *revs,
-+ uint32_t gen)
++ uint32_t gen_cutoff)
+{
+ struct topo_walk_info *info = revs->topo_walk_info;
+ struct commit *c;
+ while ((c = prio_queue_peek(&info->explore_queue)) &&
-+ c->generation >= gen)
++ c->generation >= gen_cutoff)
+ explore_walk_step(revs);
+}
+
@@ -266,9 +267,6 @@
+
+ explore_to_depth(revs, c->generation);
+
-+ if (parse_commit_gently(c, 1) < 0)
-+ return;
-+
+ for (p = c->parents; p; p = p->next) {
+ struct commit *parent = p->item;
+ int *pi = indegree_slab_at(&info->indegree, parent);
@@ -285,12 +283,13 @@
+ }
+}
+
-+static void compute_indegrees_to_depth(struct rev_info *revs)
++static void compute_indegrees_to_depth(struct rev_info *revs,
++ uint32_t gen_cutoff)
+{
+ struct topo_walk_info *info = revs->topo_walk_info;
+ struct commit *c;
+ while ((c = prio_queue_peek(&info->indegree_queue)) &&
-+ c->generation >= info->min_generation)
++ c->generation >= gen_cutoff)
+ indegree_walk_step(revs);
+}
@@ -305,9 +304,9 @@
- limit_list(revs);
- sort_in_topological_order(&revs->commits, revs->sort_order);
+ init_indegree_slab(&info->indegree);
-+ memset(&info->explore_queue, '\0', sizeof(info->explore_queue));
-+ memset(&info->indegree_queue, '\0', sizeof(info->indegree_queue));
-+ memset(&info->topo_queue, '\0', sizeof(info->topo_queue));
++ memset(&info->explore_queue, 0, sizeof(info->explore_queue));
++ memset(&info->indegree_queue, 0, sizeof(info->indegree_queue));
++ memset(&info->topo_queue, 0, sizeof(info->topo_queue));
+
+ switch (revs->sort_order) {
+ default: /* REV_SORT_IN_GRAPH_ORDER */
@@ -329,23 +328,22 @@
+ info->min_generation = GENERATION_NUMBER_INFINITY;
+ for (list = revs->commits; list; list = list->next) {
+ struct commit *c = list->item;
-+ test_flag_and_insert(&info->explore_queue, c, TOPO_WALK_EXPLORED);
-+ test_flag_and_insert(&info->indegree_queue, c, TOPO_WALK_INDEGREE);
+
+ if (parse_commit_gently(c, 1))
+ continue;
++
++ test_flag_and_insert(&info->explore_queue, c, TOPO_WALK_EXPLORED);
++ test_flag_and_insert(&info->indegree_queue, c, TOPO_WALK_INDEGREE);
++
+ if (c->generation < info->min_generation)
+ info->min_generation = c->generation;
-+ }
+
-+ for (list = revs->commits; list; list = list->next) {
-+ struct commit *c = list->item;
+ *(indegree_slab_at(&info->indegree, c)) = 1;
+
+ if (revs->sort_order == REV_SORT_BY_AUTHOR_DATE)
+ record_author_date(&info->author_date, c);
+ }
-+ compute_indegrees_to_depth(revs);
++ compute_indegrees_to_depth(revs, info->min_generation);
+
+ for (list = revs->commits; list; list = list->next) {
+ struct commit *c = list->item;
@@ -385,9 +383,8 @@
+ if (process_parents(revs, commit, NULL, NULL) < 0) {
if (!revs->ignore_missing_links)
die("Failed to traverse parents of commit %s",
-- oid_to_hex(&commit->object.oid));
-+ oid_to_hex(&commit->object.oid));
-+ }
+ oid_to_hex(&commit->object.oid));
+ }
+
+ for (p = commit->parents; p; p = p->next) {
+ struct commit *parent = p->item;
@@ -398,7 +395,7 @@
+
+ if (parent->generation < info->min_generation) {
+ info->min_generation = parent->generation;
-+ compute_indegrees_to_depth(revs);
++ compute_indegrees_to_depth(revs, info->min_generation);
+ }
+
+ pi = indegree_slab_at(&info->indegree, parent);
@@ -409,9 +406,10 @@
+
+ if (revs->first_parent_only)
+ return;
- }
++ }
}
+ int prepare_revision_walk(struct rev_info *revs)
diff --git a/revision.h b/revision.h
--- a/revision.h
7: a21febe112 = 7: 5479087812 t6012: make rev-list tests more interesting
