describe: use prio_queue
Replace the use a list-based priority queue whose order is maintained by commit_list_insert_by_date() with a prio_queue. This avoids quadratic worst-case complexity. And in the somewhat contrived example of describing the 4751 commits from v2.41.0 to v2.47.0 in one go (to get a sizable chunk of describe work with minimal ref loading overhead) it's significantly faster: Benchmark 1: ./git_2.50.1 describe $(git rev-list v2.41.0..v2.47.0) Time (mean ± σ): 1.558 s ± 0.002 s [User: 1.492 s, System: 0.051 s] Range (min … max): 1.557 s … 1.562 s 10 runs Benchmark 2: ./git describe $(git rev-list v2.41.0..v2.47.0) Time (mean ± σ): 1.209 s ± 0.006 s [User: 1.143 s, System: 0.051 s] Range (min … max): 1.201 s … 1.219 s 10 runs Summary ./git describe $(git rev-list v2.41.0..v2.47.0) ran 1.29 ± 0.01 times faster than ./git_2.50.1 describe $(git rev-list v2.41.0..v2.47.0) Signed-off-by: René Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
René Scharfe committed
Aug 3, 2025 at 13:38 UTC
66e2adb8f6fe97bb480d96205fb3473b8c1fe4df
1 file changed
+27
-24
builtin/describe.c
+27
-24
@@ -23,6 +23,7 @@
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#include "list-objects.h"
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#include "commit-slab.h"
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#include "wildmatch.h"
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+#include "prio-queue.h"
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#define MAX_TAGS (FLAG_BITS - 1)
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#define DEFAULT_CANDIDATES 10
@@ -249,24 +250,26 @@ static int compare_pt(const void *a_, const void *b_)
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return 0;
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}
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-static unsigned long finish_depth_computation(
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- struct commit_list **list,
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- struct possible_tag *best)
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+static bool all_have_flag(const struct prio_queue *queue, unsigned flag)
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+{
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+ for (size_t i = 0; i < queue->nr; i++) {
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+ struct commit *commit = queue->array[i].data;
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+ if (!(commit->object.flags & flag))
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+ return false;
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+ }
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+ return true;
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+}
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+
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+static unsigned long finish_depth_computation(struct prio_queue *queue,
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+ struct possible_tag *best)
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{
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unsigned long seen_commits = 0;
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- while (*list) {
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- struct commit *c = pop_commit(list);
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+ while (queue->nr) {
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+ struct commit *c = prio_queue_get(queue);
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struct commit_list *parents = c->parents;
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seen_commits++;
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if (c->object.flags & best->flag_within) {
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- struct commit_list *a = *list;
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- while (a) {
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- struct commit *i = a->item;
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- if (!(i->object.flags & best->flag_within))
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- break;
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- a = a->next;
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- }
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- if (!a)
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+ if (all_have_flag(queue, best->flag_within))
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break;
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} else
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best->depth++;
@@ -274,7 +277,7 @@ static unsigned long finish_depth_computation(
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struct commit *p = parents->item;
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repo_parse_commit(the_repository, p);
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if (!(p->object.flags & SEEN))
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- commit_list_insert_by_date(p, list);
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+ prio_queue_put(queue, p);
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p->object.flags |= c->object.flags;
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parents = parents->next;
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}
@@ -316,7 +319,7 @@ static void append_suffix(int depth, const struct object_id *oid, struct strbuf
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static void describe_commit(struct object_id *oid, struct strbuf *dst)
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{
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struct commit *cmit, *gave_up_on = NULL;
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- struct commit_list *list;
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+ struct prio_queue queue = { compare_commits_by_commit_date };
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struct commit_name *n;
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struct possible_tag all_matches[MAX_TAGS];
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unsigned int match_cnt = 0, annotated_cnt = 0, cur_match;
@@ -359,11 +362,10 @@ static void describe_commit(struct object_id *oid, struct strbuf *dst)
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have_util = 1;
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}
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- list = NULL;
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cmit->object.flags = SEEN;
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- commit_list_insert(cmit, &list);
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- while (list) {
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- struct commit *c = pop_commit(&list);
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+ prio_queue_put(&queue, cmit);
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+ while (queue.nr) {
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+ struct commit *c = prio_queue_get(&queue);
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struct commit_list *parents = c->parents;
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struct commit_name **slot;
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@@ -397,7 +399,7 @@ static void describe_commit(struct object_id *oid, struct strbuf *dst)
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t->depth++;
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}
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/* Stop if last remaining path already covered by best candidate(s) */
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- if (annotated_cnt && !list) {
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+ if (annotated_cnt && !queue.nr) {
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int best_depth = INT_MAX;
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unsigned best_within = 0;
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for (cur_match = 0; cur_match < match_cnt; cur_match++) {
@@ -420,7 +422,7 @@ static void describe_commit(struct object_id *oid, struct strbuf *dst)
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struct commit *p = parents->item;
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repo_parse_commit(the_repository, p);
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if (!(p->object.flags & SEEN))
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- commit_list_insert_by_date(p, &list);
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+ prio_queue_put(&queue, p);
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p->object.flags |= c->object.flags;
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parents = parents->next;
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@@ -435,6 +437,7 @@ static void describe_commit(struct object_id *oid, struct strbuf *dst)
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strbuf_add_unique_abbrev(dst, cmit_oid, abbrev);
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if (suffix)
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strbuf_addstr(dst, suffix);
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+ clear_prio_queue(&queue);
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return;
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}
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if (unannotated_cnt)
@@ -450,11 +453,11 @@ static void describe_commit(struct object_id *oid, struct strbuf *dst)
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QSORT(all_matches, match_cnt, compare_pt);
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if (gave_up_on) {
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- commit_list_insert_by_date(gave_up_on, &list);
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+ prio_queue_put(&queue, gave_up_on);
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seen_commits--;
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}
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- seen_commits += finish_depth_computation(&list, &all_matches[0]);
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- free_commit_list(list);
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+ seen_commits += finish_depth_computation(&queue, &all_matches[0]);
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+ clear_prio_queue(&queue);
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if (debug) {
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static int label_width = -1;