[PATCH v3 4/8] commit-reach: add trace2 instrumentation to paint_down_to_common()

["Kristofer Karlsson via GitGitGadget" <gitgitgadget@gmail.com>]

From: Kristofer Karlsson <krka@spotify.com>

Add a step counter and trace2_data_intmax() call so that the number
of commits visited during the paint walk is observable via
GIT_TRACE2_EVENT. This provides a way to measure the impact of
future optimizations without relying on wall-clock benchmarks alone.

Signed-off-by: Kristofer Karlsson <krka@spotify.com>
---
 commit-reach.c        |  5 ++++
 t/t6600-test-reach.sh | 53 ++++++++++++++++++++++++++++++-------------
 2 files changed, 42 insertions(+), 16 deletions(-)

diff --git a/commit-reach.c b/commit-reach.c
index a9483759e0..f6a438550b 100644
--- a/commit-reach.c
+++ b/commit-reach.c
@@ -11,6 +11,7 @@
 #include "tag.h"
 #include "commit-reach.h"
 #include "ewah/ewok.h"
+#include "trace2.h"
 
 /* Remember to update object flag allocation in object.h */
 #define PARENT1		(1u<<16)
@@ -112,6 +113,7 @@ static int paint_down_to_common(struct repository *r,
 		{ compare_commits_by_gen_then_commit_date }
 	};
 	int i;
+	int steps = 0;
 	timestamp_t last_gen = GENERATION_NUMBER_INFINITY;
 	struct commit_list **tail = result;
 
@@ -135,6 +137,7 @@ static int paint_down_to_common(struct repository *r,
 		struct commit_list *parents;
 		int flags;
 		timestamp_t generation = commit_graph_generation(commit);
+		steps++;
 
 		if (min_generation && generation > last_gen)
 			BUG("bad generation skip %"PRItime" > %"PRItime" at %s",
@@ -190,6 +193,8 @@ static int paint_down_to_common(struct repository *r,
 	}
 
 	clear_nonstale_queue(&queue);
+	trace2_data_intmax("paint_down_to_common", r,
+			   "steps", steps);
 	commit_list_sort_by_date(result);
 	return 0;
 }
diff --git a/t/t6600-test-reach.sh b/t/t6600-test-reach.sh
index 4b771b4c58..b3a31b80ac 100755
--- a/t/t6600-test-reach.sh
+++ b/t/t6600-test-reach.sh
@@ -118,24 +118,34 @@ test_expect_success 'setup' '
 '
 
 run_all_modes () {
-	test_when_finished rm -rf .git/objects/info/commit-graph &&
-	"$@" <input >actual &&
-	test_cmp expect actual &&
-	cp commit-graph-full .git/objects/info/commit-graph &&
-	"$@" <input >actual &&
-	test_cmp expect actual &&
-	cp commit-graph-half .git/objects/info/commit-graph &&
-	"$@" <input >actual &&
-	test_cmp expect actual &&
-	cp commit-graph-no-gdat .git/objects/info/commit-graph &&
-	"$@" <input >actual &&
-	test_cmp expect actual
+	graph=.git/objects/info/commit-graph &&
+	test_when_finished rm -rf "$graph" "${graph}s" &&
+	rm -f trace-mode-*.txt &&
+
+	for mode in none full half no-gdat
+	do
+		rm -rf "$graph" "${graph}s" &&
+		cp "commit-graph-${mode}" "$graph" 2>/dev/null ||
+		true &&
+		GIT_TRACE2_EVENT="$(pwd)/trace-mode-${mode}.txt" \
+			"$@" <input >actual &&
+		test_cmp expect actual || return 1
+	done
 }
 
 test_all_modes () {
 	run_all_modes test-tool reach "$@"
 }
 
+test_paint_down_steps () {
+	for mode in none full half no-gdat
+	do
+		test_trace2_data paint_down_to_common steps "$1" \
+			<"trace-mode-${mode}.txt" || return 1
+		shift
+	done
+}
+
 test_expect_success 'ref_newer:miss' '
 	cat >input <<-\EOF &&
 	A:commit-5-7
@@ -209,7 +219,8 @@ test_expect_success 'in_merge_bases_many:self' '
 	X:commit-6-8
 	EOF
 	echo "in_merge_bases_many(A,X):1" >expect &&
-	test_all_modes in_merge_bases_many
+	test_all_modes in_merge_bases_many &&
+	test_paint_down_steps 45 2 25 3
 '
 
 test_expect_success 'is_descendant_of:hit' '
@@ -277,7 +288,8 @@ test_expect_success 'get_merge_bases_many:pending-stale' '
 		echo "get_merge_bases_many(A,X):" &&
 		git rev-parse ps-B
 	} >expect &&
-	test_all_modes get_merge_bases_many
+	test_all_modes get_merge_bases_many &&
+	test_paint_down_steps 6 6 6 6
 '
 
 test_expect_success 'get_merge_bases_many:infinity-both-sides' '
@@ -291,7 +303,8 @@ test_expect_success 'get_merge_bases_many:infinity-both-sides' '
 		echo "get_merge_bases_many(A,X):" &&
 		git rev-parse pi-B
 	} >expect &&
-	test_all_modes get_merge_bases_many
+	test_all_modes get_merge_bases_many &&
+	test_paint_down_steps 5 5 5 5
 '
 
 test_expect_success 'setup mixed finite/INFINITY topology' '
@@ -316,7 +329,15 @@ test_expect_success 'get_merge_bases_many:mixed-finite-infinity' '
 		echo "get_merge_bases_many(A,X):" &&
 		git rev-parse ps-X
 	} >expect &&
-	test_all_modes get_merge_bases_many
+	test_all_modes get_merge_bases_many &&
+	test_paint_down_steps 3 3 3 3
+'
+
+test_expect_success 'merge-base --all commit-walk steps' '
+	>input &&
+	git rev-parse commit-9-1 >expect &&
+	run_all_modes git merge-base --all commit-9-9 commit-9-1 &&
+	test_paint_down_steps 81 80 81 81
 '
 
 test_expect_success 'reduce_heads' '
-- 
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