[PATCH v2 2/2] skip_verify_index: helper test

[git@jeffhostetler.com]

From: Jeff Hostetler <jeffhost@microsoft.com>

Created test to measure read_index() with and without
skip_verify_index set and report performance differences.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
---
 Makefile                          |  1 +
 t/helper/.gitignore               |  1 +
 t/helper/test-skip-verify-index.c | 73 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 75 insertions(+)
 create mode 100644 t/helper/test-skip-verify-index.c

diff --git a/Makefile b/Makefile
index 9ec6065..e4932b6 100644
--- a/Makefile
+++ b/Makefile
@@ -631,6 +631,7 @@ TEST_PROGRAMS_NEED_X += test-scrap-cache-tree
 TEST_PROGRAMS_NEED_X += test-sha1
 TEST_PROGRAMS_NEED_X += test-sha1-array
 TEST_PROGRAMS_NEED_X += test-sigchain
+TEST_PROGRAMS_NEED_X += test-skip-verify-index
 TEST_PROGRAMS_NEED_X += test-string-list
 TEST_PROGRAMS_NEED_X += test-submodule-config
 TEST_PROGRAMS_NEED_X += test-subprocess
diff --git a/t/helper/.gitignore b/t/helper/.gitignore
index d6e8b36..4d2ed3c 100644
--- a/t/helper/.gitignore
+++ b/t/helper/.gitignore
@@ -25,6 +25,7 @@
 /test-sha1
 /test-sha1-array
 /test-sigchain
+/test-skip-verify-index
 /test-string-list
 /test-submodule-config
 /test-subprocess
diff --git a/t/helper/test-skip-verify-index.c b/t/helper/test-skip-verify-index.c
new file mode 100644
index 0000000..ec2db27
--- /dev/null
+++ b/t/helper/test-skip-verify-index.c
@@ -0,0 +1,73 @@
+#include "cache.h"
+#include "parse-options.h"
+
+uint64_t time_runs(int count)
+{
+	uint64_t t0, t1;
+	uint64_t sum = 0;
+	uint64_t avg;
+	int i;
+
+	for (i = 0; i < count; i++) {
+		t0 = getnanotime();
+		read_cache();
+		t1 = getnanotime();
+
+		sum += (t1 - t0);
+
+		printf("%f %d [cache_nr %d]\n",
+			   ((double)(t1 - t0))/1000000000,
+			   skip_verify_index,
+			   the_index.cache_nr);
+		fflush(stdout);
+
+		discard_cache();
+	}
+
+	avg = sum / count;
+	if (count > 1) {
+		printf("%f %d avg\n",
+			   (double)avg/1000000000,
+			   skip_verify_index);
+		fflush(stdout);
+	}
+
+	return avg;
+}
+
+int cmd_main(int argc, const char **argv)
+{
+	int count = 1;
+	const char *usage[] = {
+		"test-core-verify-index",
+		NULL
+	};
+	struct option options[] = {
+		OPT_INTEGER('c', "count", &count, "number of passes"),
+		OPT_END(),
+	};
+	const char *prefix;
+	uint64_t avg_no_skip, avg_skip;
+
+	prefix = setup_git_directory();
+	argc = parse_options(argc, argv, prefix, options, usage, 0);
+
+	if (count < 1)
+		die("count must greater than zero");
+
+	/* throw away call to get the index in the disk cache */
+	read_cache();
+	discard_cache();
+
+	/* disable index SHA verification */
+	skip_verify_index = 0;
+	avg_no_skip = time_runs(count);
+
+	/* enable index SHA verification */
+	skip_verify_index = 1;
+	avg_skip = time_runs(count);
+
+	if (avg_skip > avg_no_skip)
+		die("skipping index SHA verification did not help");
+	return 0;
+}
-- 
2.7.4