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commit-graph: add trace2 instrumentation for generation DFS

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Count the number of steps taken in
compute_reachable_generation_numbers() and expose it via
trace2 to make it easier to detect performance regressions.

Add a failing test for such a regression, introduced in
199d452758 (commit-graph: return the prepared commit graph
from `prepare_commit_graph()`, 2025-09-04), where incremental
commit-graph writes do not see existing generation numbers
from lower graph layers and fall back to walking the full
ancestry.

Signed-off-by: Kristofer Karlsson <krka@spotify.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Kristofer Karlsson
2026-07-09 15:03:00 +00:00
committed by Junio C Hamano
parent f85a7e6620
commit 02d62c33be
2 changed files with 29 additions and 0 deletions
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5
commit-graph.c
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@@ -1653,6 +1653,7 @@ static void compute_reachable_generation_numbers(
{
int i;
struct commit_list *list = NULL;
intmax_t steps = 0;
for (i = 0; i < info->commits->nr; i++) {
struct commit *c = info->commits->items[i];
@@ -1671,6 +1672,7 @@ static void compute_reachable_generation_numbers(
int all_parents_computed = 1;
timestamp_t max_gen = 0;
steps++;
for (parent = current->parents; parent; parent = parent->next) {
repo_parse_commit(info->r, parent->item);
gen = info->get_generation(parent->item, info->data);
@@ -1694,6 +1696,9 @@ static void compute_reachable_generation_numbers(
}
}
}
trace2_data_intmax("commit-graph", info->r,
"generation-dfs-steps", steps);
}
static timestamp_t get_topo_level(struct commit *c, void *data)