pop_most_recent_commit() calls commit_list_insert_by_date() for parent
commits, which is itself called in a loop. This can lead to quadratic
complexity if there are many merges. Replace the commit_list with a
prio_queue to ensure logarithmic worst case complexity and convert all
three users.
Add a performance test that exercises one of them using a pathological
history that consists of 50% merges and 50% root commits to demonstrate
the speedup:
Test v2.50.1 HEAD
----------------------------------------------------------------------
1501.2: rev-parse ':/65535' 2.48(2.47+0.00) 0.20(0.19+0.00) -91.9%
Alas, sane histories don't benefit from the conversion much, and
traversing Git's own history takes a 1% performance hit on my machine:
$ hyperfine -w3 -L git ./git_2.50.1,./git '{git} rev-parse :/^Initial.revision'
Benchmark 1: ./git_2.50.1 rev-parse :/^Initial.revision
Time (mean ± σ): 1.071 s ± 0.004 s [User: 1.052 s, System: 0.017 s]
Range (min … max): 1.067 s … 1.078 s 10 runs
Benchmark 2: ./git rev-parse :/^Initial.revision
Time (mean ± σ): 1.079 s ± 0.003 s [User: 1.060 s, System: 0.017 s]
Range (min … max): 1.074 s … 1.083 s 10 runs
Summary
./git_2.50.1 rev-parse :/^Initial.revision ran
1.01 ± 0.00 times faster than ./git rev-parse :/^Initial.revision
Signed-off-by: René Scharfe <l.s.r@xxxxxx>
---
commit.c | 7 +--
commit.h | 8 ++--
fetch-pack.c | 13 +++---
object-name.c | 10 ++---
t/meson.build | 1 +
t/perf/p1501-rev-parse-oneline.sh | 71 +++++++++++++++++++++++++++++++
walker.c | 11 +++--
7 files changed, 100 insertions(+), 21 deletions(-)
create mode 100755 t/perf/p1501-rev-parse-oneline.sh
diff --git a/commit.c b/commit.c
index 15115125c3..f4712ad9a7 100644
--- a/commit.c
+++ b/commit.c
@@ -31,6 +31,7 @@
#include "parse.h"
#include "object-file.h"
#include "object-file-convert.h"
+#include "prio-queue.h"
static struct commit_extra_header *read_commit_extra_header_lines(const char *buf, size_t len, const char **);
@@ -739,17 +740,17 @@ void commit_list_sort_by_date(struct commit_list **list)
commit_list_sort(list, commit_list_compare_by_date);
}
-struct commit *pop_most_recent_commit(struct commit_list **list,
+struct commit *pop_most_recent_commit(struct prio_queue *queue,
unsigned int mark)
{
- struct commit *ret = pop_commit(list);
+ struct commit *ret = prio_queue_get(queue);
struct commit_list *parents = ret->parents;
while (parents) {
struct commit *commit = parents->item;
if (!repo_parse_commit(the_repository, commit) && !(commit->object.flags & mark)) {
commit->object.flags |= mark;
- commit_list_insert_by_date(commit, list);
+ prio_queue_put(queue, commit);
}
parents = parents->next;
}
diff --git a/commit.h b/commit.h
index 70c870dae4..9630c076d6 100644
--- a/commit.h
+++ b/commit.h
@@ -201,10 +201,10 @@ const char *repo_logmsg_reencode(struct repository *r,
const char *skip_blank_lines(const char *msg);
-/** Removes the first commit from a list sorted by date, and adds all
- * of its parents.
- **/
-struct commit *pop_most_recent_commit(struct commit_list **list,
+struct prio_queue;
+
+/* Removes the first commit from a prio_queue and adds its parents. */
+struct commit *pop_most_recent_commit(struct prio_queue *queue,
unsigned int mark);
struct commit *pop_commit(struct commit_list **stack);
diff --git a/fetch-pack.c b/fetch-pack.c
index 5e74235fc0..8ad5bf2931 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -34,6 +34,7 @@
#include "commit-graph.h"
#include "sigchain.h"
#include "mergesort.h"
+#include "prio-queue.h"
static int transfer_unpack_limit = -1;
static int fetch_unpack_limit = -1;
@@ -601,7 +602,7 @@ static int find_common(struct fetch_negotiator *negotiator,
return count ? retval : 0;
}
-static struct commit_list *complete;
+static struct prio_queue complete = { compare_commits_by_commit_date };
static int mark_complete(const struct object_id *oid)
{
@@ -609,7 +610,7 @@ static int mark_complete(const struct object_id *oid)
if (commit && !(commit->object.flags & COMPLETE)) {
commit->object.flags |= COMPLETE;
- commit_list_insert(commit, &complete);
+ prio_queue_put(&complete, commit);
}
return 0;
}
@@ -626,9 +627,12 @@ static int mark_complete_oid(const char *refname UNUSED,
static void mark_recent_complete_commits(struct fetch_pack_args *args,
timestamp_t cutoff)
{
- while (complete && cutoff <= complete->item->date) {
+ while (complete.nr) {
+ struct commit *item = prio_queue_peek(&complete);
+ if (item->date < cutoff)
+ break;
print_verbose(args, _("Marking %s as complete"),
- oid_to_hex(&complete->item->object.oid));
+ oid_to_hex(&item->object.oid));
pop_most_recent_commit(&complete, COMPLETE);
}
}
@@ -798,7 +802,6 @@ static void mark_complete_and_common_ref(struct fetch_negotiator *negotiator,
refs_for_each_rawref(get_main_ref_store(the_repository),
mark_complete_oid, NULL);
for_each_cached_alternate(NULL, mark_alternate_complete);
- commit_list_sort_by_date(&complete);
if (cutoff)
mark_recent_complete_commits(args, cutoff);
}
diff --git a/object-name.c b/object-name.c
index ddafe7f9b1..41930609e3 100644
--- a/object-name.c
+++ b/object-name.c
@@ -28,6 +28,7 @@
#include "commit-reach.h"
#include "date.h"
#include "object-file-convert.h"
+#include "prio-queue.h"
static int get_oid_oneline(struct repository *r, const char *, struct object_id *,
const struct commit_list *);
@@ -1461,7 +1462,7 @@ static int get_oid_oneline(struct repository *r,
const char *prefix, struct object_id *oid,
const struct commit_list *list)
{
- struct commit_list *copy = NULL, **copy_tail = ©
+ struct prio_queue copy = { compare_commits_by_commit_date };
const struct commit_list *l;
int found = 0;
int negative = 0;
@@ -1483,9 +1484,9 @@ static int get_oid_oneline(struct repository *r,
for (l = list; l; l = l->next) {
l->item->object.flags |= ONELINE_SEEN;
- copy_tail = &commit_list_insert(l->item, copy_tail)->next;
+ prio_queue_put(©, l->item);
}
- while (copy) {
+ while (copy.nr) {
const char *p, *buf;
struct commit *commit;
int matches;
@@ -1507,7 +1508,7 @@ static int get_oid_oneline(struct repository *r,
regfree(®ex);
for (l = list; l; l = l->next)
clear_commit_marks(l->item, ONELINE_SEEN);
- free_commit_list(copy);
+ clear_prio_queue(©);
return found ? 0 : -1;
}
@@ -2061,7 +2062,6 @@ static enum get_oid_result get_oid_with_context_1(struct repository *repo,
cb.list = &list;
refs_for_each_ref(get_main_ref_store(repo), handle_one_ref, &cb);
refs_head_ref(get_main_ref_store(repo), handle_one_ref, &cb);
- commit_list_sort_by_date(&list);
ret = get_oid_oneline(repo, name + 2, oid, list);
free_commit_list(list);
diff --git a/t/meson.build b/t/meson.build
index 1af289425d..660d780dcc 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -1116,6 +1116,7 @@ benchmarks = [
'perf/p1450-fsck.sh',
'perf/p1451-fsck-skip-list.sh',
'perf/p1500-graph-walks.sh',
+ 'perf/p1501-rev-parse-oneline.sh',
'perf/p2000-sparse-operations.sh',
'perf/p3400-rebase.sh',
'perf/p3404-rebase-interactive.sh',
diff --git a/t/perf/p1501-rev-parse-oneline.sh b/t/perf/p1501-rev-parse-oneline.sh
new file mode 100755
index 0000000000..538fa9c404
--- /dev/null
+++ b/t/perf/p1501-rev-parse-oneline.sh
@@ -0,0 +1,71 @@
+#!/bin/sh
+
+test_description='Test :/ object name notation'
+
+. ./perf-lib.sh
+
+test_perf_fresh_repo
+
+#
+# Creates lots of merges to make history traversal costly. In
+# particular it creates 2^($max_level-1)-1 2-way merges on top of
+# 2^($max_level-1) root commits. E.g., the commit history looks like
+# this for a $max_level of 3:
+#
+# _1_
+# / \
+# 2 3
+# / \ / \
+# 4 5 6 7
+#
+# The numbers are the fast-import marks, which also are the commit
+# messages. 1 is the HEAD commit and a merge, 2 and 3 are also merges,
+# 4-7 are the root commits.
+#
+build_history () {
+ local max_level="$1" &&
+ local level="${2:-1}" &&
+ local mark="${3:-1}" &&
+ if test $level -eq $max_level
+ then
+ echo "reset refs/heads/master" &&
+ echo "from $ZERO_OID" &&
+ echo "commit refs/heads/master" &&
+ echo "mark :$mark" &&
+ echo "committer C <c@xxxxxxxxxxx> 1234567890 +0000" &&
+ echo "data <<EOF" &&
+ echo "$mark" &&
+ echo "EOF"
+ else
+ local level1=$((level+1)) &&
+ local mark1=$((2*mark)) &&
+ local mark2=$((2*mark+1)) &&
+ build_history $max_level $level1 $mark1 &&
+ build_history $max_level $level1 $mark2 &&
+ echo "commit refs/heads/master" &&
+ echo "mark :$mark" &&
+ echo "committer C <c@xxxxxxxxxxx> 1234567890 +0000" &&
+ echo "data <<EOF" &&
+ echo "$mark" &&
+ echo "EOF" &&
+ echo "from :$mark1" &&
+ echo "merge :$mark2"
+ fi
+}
+
+test_expect_success 'setup' '
+ build_history 16 | git fast-import &&
+ git log --format="%H %s" --reverse >commits &&
+ sed -n -e "s/ .*$//p" -e "q" <commits >expect &&
+ sed -n -e "s/^.* //p" -e "q" <commits >needle
+'
+
+test_perf "rev-parse :/$(cat needle)" '
+ git rev-parse :/$(cat needle) >actual
+'
+
+test_expect_success 'verify result' '
+ test_cmp expect actual
+'
+
+test_done
diff --git a/walker.c b/walker.c
index d131af04c7..8073754517 100644
--- a/walker.c
+++ b/walker.c
@@ -14,6 +14,7 @@
#include "blob.h"
#include "refs.h"
#include "progress.h"
+#include "prio-queue.h"
static struct object_id current_commit_oid;
@@ -78,7 +79,7 @@ static int process_tree(struct walker *walker, struct tree *tree)
#define SEEN (1U << 1)
#define TO_SCAN (1U << 2)
-static struct commit_list *complete = NULL;
+static struct prio_queue complete = { compare_commits_by_commit_date };
static int process_commit(struct walker *walker, struct commit *commit)
{
@@ -87,7 +88,10 @@ static int process_commit(struct walker *walker, struct commit *commit)
if (repo_parse_commit(the_repository, commit))
return -1;
- while (complete && complete->item->date >= commit->date) {
+ while (complete.nr) {
+ struct commit *item = prio_queue_peek(&complete);
+ if (item->date < commit->date)
+ break;
pop_most_recent_commit(&complete, COMPLETE);
}
@@ -233,7 +237,7 @@ static int mark_complete(const char *path UNUSED,
if (commit) {
commit->object.flags |= COMPLETE;
- commit_list_insert(commit, &complete);
+ prio_queue_put(&complete, commit);
}
return 0;
}
@@ -302,7 +306,6 @@ int walker_fetch(struct walker *walker, int targets, char **target,
if (!walker->get_recover) {
refs_for_each_ref(get_main_ref_store(the_repository),
mark_complete, NULL);
- commit_list_sort_by_date(&complete);
}
for (i = 0; i < targets; i++) {
--
2.50.1
