fsmonitor: add a performance test

Add a test utility (test-drop-caches) that flushes all changes to disk
then drops file system cache on Windows, Linux, and OSX.

Add a perf test (p7519-fsmonitor.sh) for fsmonitor.

By default, the performance test will utilize the Watchman file system
monitor if it is installed.  If Watchman is not installed, it will use a
dummy integration script that does not report any new or modified files.
The dummy script has very little overhead which provides optimistic results.

The performance test will also use the untracked cache feature if it is
available as fsmonitor uses it to speed up scanning for untracked files.

There are 4 environment variables that can be used to alter the default
behavior of the performance test:

GIT_PERF_7519_UNTRACKED_CACHE: used to configure core.untrackedCache
GIT_PERF_7519_SPLIT_INDEX: used to configure core.splitIndex
GIT_PERF_7519_FSMONITOR: used to configure core.fsmonitor
GIT_PERF_7519_DROP_CACHE: if set, the OS caches are dropped between tests

The big win for using fsmonitor is the elimination of the need to scan the
working directory looking for changed and untracked files. If the file
information is all cached in RAM, the benefits are reduced.

Signed-off-by: Ben Peart <benpeart@microsoft.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 184 insertions, 0 deletions

diff --git a/t/perf/p7519-fsmonitor.sh b/t/perf/p7519-fsmonitor.sh
new file mode 100755
index 0000000000..16d1bf72e5
--- /dev/null
+++ b/t/perf/p7519-fsmonitor.sh
@@ -0,0 +1,184 @@
+#!/bin/sh
+
+test_description="Test core.fsmonitor"
+
+. ./perf-lib.sh
+
+#
+# Performance test for the fsmonitor feature which enables git to talk to a
+# file system change monitor and avoid having to scan the working directory
+# for new or modified files.
+#
+# By default, the performance test will utilize the Watchman file system
+# monitor if it is installed.  If Watchman is not installed, it will use a
+# dummy integration script that does not report any new or modified files.
+# The dummy script has very little overhead which provides optimistic results.
+#
+# The performance test will also use the untracked cache feature if it is
+# available as fsmonitor uses it to speed up scanning for untracked files.
+#
+# There are 3 environment variables that can be used to alter the default
+# behavior of the performance test:
+#
+# GIT_PERF_7519_UNTRACKED_CACHE: used to configure core.untrackedCache
+# GIT_PERF_7519_SPLIT_INDEX: used to configure core.splitIndex
+# GIT_PERF_7519_FSMONITOR: used to configure core.fsMonitor
+#
+# The big win for using fsmonitor is the elimination of the need to scan the
+# working directory looking for changed and untracked files. If the file
+# information is all cached in RAM, the benefits are reduced.
+#
+# GIT_PERF_7519_DROP_CACHE: if set, the OS caches are dropped between tests
+#
+
+test_perf_large_repo
+test_checkout_worktree
+
+test_lazy_prereq UNTRACKED_CACHE '
+	{ git update-index --test-untracked-cache; ret=$?; } &&
+	test $ret -ne 1
+'
+
+test_lazy_prereq WATCHMAN '
+	{ command -v watchman >/dev/null 2>&1; ret=$?; } &&
+	test $ret -ne 1
+'
+
+if test_have_prereq WATCHMAN
+then
+	# Convert unix style paths to escaped Windows style paths for Watchman
+	case "$(uname -s)" in
+	MSYS_NT*)
+	  GIT_WORK_TREE="$(cygpath -aw "$PWD" | sed 's,\\,/,g')"
+	  ;;
+	*)
+	  GIT_WORK_TREE="$PWD"
+	  ;;
+	esac
+fi
+
+if test -n "$GIT_PERF_7519_DROP_CACHE"
+then
+	# When using GIT_PERF_7519_DROP_CACHE, GIT_PERF_REPEAT_COUNT must be 1 to
+	# generate valid results. Otherwise the caching that happens for the nth
+	# run will negate the validity of the comparisons.
+	if test "$GIT_PERF_REPEAT_COUNT" -ne 1
+	then
+		echo "warning: Setting GIT_PERF_REPEAT_COUNT=1" >&2
+		GIT_PERF_REPEAT_COUNT=1
+	fi
+fi
+
+test_expect_success "setup for fsmonitor" '
+	# set untrackedCache depending on the environment
+	if test -n "$GIT_PERF_7519_UNTRACKED_CACHE"
+	then
+		git config core.untrackedCache "$GIT_PERF_7519_UNTRACKED_CACHE"
+	else
+		if test_have_prereq UNTRACKED_CACHE
+		then
+			git config core.untrackedCache true
+		else
+			git config core.untrackedCache false
+		fi
+	fi &&
+
+	# set core.splitindex depending on the environment
+	if test -n "$GIT_PERF_7519_SPLIT_INDEX"
+	then
+		git config core.splitIndex "$GIT_PERF_7519_SPLIT_INDEX"
+	fi &&
+
+	# set INTEGRATION_SCRIPT depending on the environment
+	if test -n "$GIT_PERF_7519_FSMONITOR"
+	then
+		INTEGRATION_SCRIPT="$GIT_PERF_7519_FSMONITOR"
+	else
+		#
+		# Choose integration script based on existence of Watchman.
+		# If Watchman exists, watch the work tree and attempt a query.
+		# If everything succeeds, use Watchman integration script,
+		# else fall back to an empty integration script.
+		#
+		mkdir .git/hooks &&
+		if test_have_prereq WATCHMAN
+		then
+			INTEGRATION_SCRIPT=".git/hooks/fsmonitor-watchman" &&
+			cp "$TEST_DIRECTORY/../templates/hooks--fsmonitor-watchman.sample" "$INTEGRATION_SCRIPT" &&
+			watchman watch "$GIT_WORK_TREE" &&
+			watchman watch-list | grep -q -F "$GIT_WORK_TREE"
+		else
+			INTEGRATION_SCRIPT=".git/hooks/fsmonitor-empty" &&
+			write_script "$INTEGRATION_SCRIPT"<<-\EOF
+			EOF
+		fi
+	fi &&
+
+	git config core.fsmonitor "$INTEGRATION_SCRIPT" &&
+	git update-index --fsmonitor
+'
+
+if test -n "$GIT_PERF_7519_DROP_CACHE"; then
+	test-drop-caches
+fi
+
+test_perf "status (fsmonitor=$INTEGRATION_SCRIPT)" '
+	git status
+'
+
+if test -n "$GIT_PERF_7519_DROP_CACHE"; then
+	test-drop-caches
+fi
+
+test_perf "status -uno (fsmonitor=$INTEGRATION_SCRIPT)" '
+	git status -uno
+'
+
+if test -n "$GIT_PERF_7519_DROP_CACHE"; then
+	test-drop-caches
+fi
+
+test_perf "status -uall (fsmonitor=$INTEGRATION_SCRIPT)" '
+	git status -uall
+'
+
+test_expect_success "setup without fsmonitor" '
+	unset INTEGRATION_SCRIPT &&
+	git config --unset core.fsmonitor &&
+	git update-index --no-fsmonitor
+'
+
+if test -n "$GIT_PERF_7519_DROP_CACHE"; then
+	test-drop-caches
+fi
+
+test_perf "status (fsmonitor=$INTEGRATION_SCRIPT)" '
+	git status
+'
+
+if test -n "$GIT_PERF_7519_DROP_CACHE"; then
+	test-drop-caches
+fi
+
+test_perf "status -uno (fsmonitor=$INTEGRATION_SCRIPT)" '
+	git status -uno
+'
+
+if test -n "$GIT_PERF_7519_DROP_CACHE"; then
+	test-drop-caches
+fi
+
+test_perf "status -uall (fsmonitor=$INTEGRATION_SCRIPT)" '
+	git status -uall
+'
+
+if test_have_prereq WATCHMAN
+then
+	watchman watch-del "$GIT_WORK_TREE" >/dev/null 2>&1 &&
+
+	# Work around Watchman bug on Windows where it holds on to handles
+	# preventing the removal of the trash directory
+	watchman shutdown-server >/dev/null 2>&1
+fi
+
+test_done