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authorJeff King <peff@peff.net>2019-09-12 01:11:37 (GMT)
committerJunio C Hamano <gitster@pobox.com>2019-09-12 18:47:30 (GMT)
commit72ed80c784e65770c4d4944b0ea54b08e098d7e3 (patch)
treebab7932d517c0cda3c336e980d2e49f83541f326 /list-objects.c
parent0d0ac3826a3bbb9247e39e12623bbcfdd722f24c (diff)
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list-objects: don't queue root trees unless revs->tree_objects is set
When traverse_commit_list() processes each commit, it queues the commit's root tree in the pending array. Then, after all commits are processed, it calls traverse_trees_and_blobs() to walk over the pending list, calling process_tree() on each. But if revs->tree_objects is not set, process_tree() just exists immediately! We can save ourselves some work by not even bothering to queue these trees in the first place. There are a few subtle points to make: - we also detect commits with a NULL tree pointer here. But this isn't an interesting check for broken commits, since the lookup_tree() we'd have done during commit parsing doesn't actually check that we have the tree on disk. So we're not losing any robustness. - besides queueing, we also set the NOT_USER_GIVEN flag on the tree object. This is used by the traverse_commit_list_filtered() variant. But if we're not exploring trees, then we won't actually care about this flag, which is used only inside process_tree() code-paths. - queueing trees eventually leads to us queueing blobs, too. But we don't need to check revs->blob_objects here. Even in the current code, we still wouldn't find those blobs, because we'd never open up the tree objects to list their contents. - the user-visible impact to the caller is minimal. The pending trees are all cleared by the time the function returns anyway, by traverse_trees_and_blobs(). We do call a show_commit() callback, which technically could be looking at revs->pending during the callback. But it seems like a rather unlikely thing to do (if you want the tree of the current commit, then accessing the tree struct member is a lot simpler). So this should be safe to do. Let's look at the benefits: [before] Benchmark #1: git -C linux rev-list HEAD >/dev/null Time (mean ± σ): 7.651 s ± 0.021 s [User: 7.399 s, System: 0.252 s] Range (min … max): 7.607 s … 7.683 s 10 runs [after] Benchmark #1: git -C linux rev-list HEAD >/dev/null Time (mean ± σ): 7.593 s ± 0.023 s [User: 7.329 s, System: 0.264 s] Range (min … max): 7.565 s … 7.634 s 10 runs Not too impressive, but then we're really just avoiding sticking a pointer into a growable array. But still, I'll take a free 0.75% speedup. Let's try it after running "git commit-graph write": [before] Benchmark #1: git -C linux rev-list HEAD >/dev/null Time (mean ± σ): 1.458 s ± 0.011 s [User: 1.199 s, System: 0.259 s] Range (min … max): 1.447 s … 1.481 s 10 runs [after] Benchmark #1: git -C linux rev-list HEAD >/dev/null Time (mean ± σ): 1.126 s ± 0.023 s [User: 896.5 ms, System: 229.0 ms] Range (min … max): 1.106 s … 1.181 s 10 runs Now that's more like it. We saved over 22% of the total time. Part of that is because the runtime is shorter overall, but the absolute improvement is also much larger. What's going on? When we fill in a commit struct using the commit graph, we don't bother to set the tree pointer, and instead lazy-load it when somebody calls get_commit_tree(). So we're not only skipping the pointer write to the pending queue, but we're skipping the lazy-load of the tree entirely. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'list-objects.c')
-rw-r--r--list-objects.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/list-objects.c b/list-objects.c
index c41cc80..5559547 100644
--- a/list-objects.c
+++ b/list-objects.c
@@ -308,7 +308,9 @@ static void do_traverse(struct traversal_context *ctx)
* an uninteresting boundary commit may not have its tree
* parsed yet, but we are not going to show them anyway
*/
- if (get_commit_tree(commit)) {
+ if (!ctx->revs->tree_objects)
+ ; /* do not bother loading tree */
+ else if (get_commit_tree(commit)) {
struct tree *tree = get_commit_tree(commit);
tree->object.flags |= NOT_USER_GIVEN;
add_pending_tree(ctx->revs, tree);