core.fsyncmethod: performance tests for batch mode

Add basic performance tests for git commands that can add data to the
object database. We cover:
* git add
* git stash
* git update-index (via git stash)
* git unpack-objects
* git commit --all

We cover all currently available fsync methods as well.

Signed-off-by: Neeraj Singh <neerajsi@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/perf/p0008-odb-fsync.sh

@@ -0,0 +1,82 @@
+#!/bin/sh
+#
+# This test measures the performance of adding new files to the object
+# database. The test was originally added to measure the effect of the
+# core.fsyncMethod=batch mode, which is why we are testing different values of
+# that setting explicitly and creating a lot of unique objects.
+
+test_description="Tests performance of adding things to the object database"
+
+. ./perf-lib.sh
+
+. $TEST_DIRECTORY/lib-unique-files.sh
+
+test_perf_fresh_repo
+test_checkout_worktree
+
+dir_count=10
+files_per_dir=50
+total_files=$((dir_count * files_per_dir))
+
+populate_files () {
+	test_create_unique_files $dir_count $files_per_dir files
+}
+
+setup_repo () {
+	(rm -rf .git || 1) &&
+	git init &&
+	test_commit first &&
+	populate_files
+}
+
+test_perf_fsync_cfgs () {
+	local method &&
+	local cfg &&
+	for method in none fsync batch writeout-only
+	do
+		case $method in
+		none)
+			cfg="-c core.fsync=none"
+			;;
+		*)
+			cfg="-c core.fsync=loose-object -c core.fsyncMethod=$method"
+		esac &&
+
+		# Set GIT_TEST_FSYNC=1 explicitly since fsync is normally
+		# disabled by t/test-lib.sh.
+		if ! test_perf "$1 (fsyncMethod=$method)" \
+						--setup "$2" \
+						"GIT_TEST_FSYNC=1 git $cfg $3"
+		then
+			break
+		fi
+	done
+}
+
+test_perf_fsync_cfgs "add $total_files files" \
+	"setup_repo" \
+	"add -- files"
+
+test_perf_fsync_cfgs "stash $total_files files" \
+	"setup_repo" \
+	"stash push -u -- files"
+
+test_perf_fsync_cfgs "unpack $total_files files" \
+	"
+	setup_repo &&
+	git -c core.fsync=none add -- files &&
+	git -c core.fsync=none commit -q -m second &&
+	echo HEAD | git pack-objects -q --stdout --revs >test_pack.pack &&
+	setup_repo
+	" \
+	"unpack-objects -q <test_pack.pack"
+
+test_perf_fsync_cfgs "commit $total_files files" \
+	"
+	setup_repo &&
+	git -c core.fsync=none add -- files &&
+	populate_files
+	" \
+	"commit -q -a -m test"
+
+test_done