[PATCH v2 09/14] lib/string_kunit: add performance benchmark for strnlen()

[Feng Jiang]

Introduce a benchmark to compare the architecture-optimized strnlen()
implementation against the generic C version (__generic_strnlen).

Suggested-by: Andy Shevchenko <andy at kernel.org>
Signed-off-by: Feng Jiang <jiangfeng at kylinos.cn>
---
 lib/tests/string_kunit.c | 48 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 47 insertions(+), 1 deletion(-)

diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
index 2266954ae5e0..6578b36213bc 100644
--- a/lib/tests/string_kunit.c
+++ b/lib/tests/string_kunit.c
@@ -20,7 +20,7 @@
 #define STRING_TEST_MAX_LEN	128
 #define STRING_TEST_MAX_OFFSET	16
 
-#if defined(__HAVE_ARCH_STRLEN)
+#if defined(__HAVE_ARCH_STRLEN) || defined(__HAVE_ARCH_STRNLEN)
 #define STRING_BENCH_ENABLED
 #endif
 
@@ -272,6 +272,49 @@ static void string_test_strnlen(struct kunit *test)
 	}
 }
 
+#ifdef __HAVE_ARCH_STRNLEN
+static void string_test_strnlen_bench(struct kunit *test)
+{
+	char *buf;
+	size_t buf_len, iters;
+	ktime_t start, end;
+	u64 time_arch, time_generic;
+
+	buf_len = get_max_bench_len(bench_cases, ARRAY_SIZE(bench_cases)) + 1;
+
+	buf = kunit_kzalloc(test, buf_len, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buf);
+
+	for (size_t i = 0; i < ARRAY_SIZE(bench_cases); i++) {
+		get_random_nonzero_bytes(buf, bench_cases[i].len);
+		buf[bench_cases[i].len] = '\0';
+
+		iters = bench_cases[i].iterations;
+
+		/* 1. Benchmark the architecture-optimized version */
+		start = ktime_get();
+		for (unsigned int j = 0; j < iters; j++) {
+			OPTIMIZER_HIDE_VAR(buf);
+			(void)strnlen(buf, buf_len);
+		}
+		end = ktime_get();
+		time_arch = ktime_to_ns(ktime_sub(end, start));
+
+		/* 2. Benchmark the generic C version */
+		start = ktime_get();
+		for (unsigned int j = 0; j < iters; j++) {
+			OPTIMIZER_HIDE_VAR(buf);
+			(void)__generic_strnlen(buf, buf_len);
+		}
+		end = ktime_get();
+		time_generic = ktime_to_ns(ktime_sub(end, start));
+
+		string_bench_report(test, "strnlen", &bench_cases[i],
+				time_arch, time_generic);
+	}
+}
+#endif
+
 static void string_test_strchr(struct kunit *test)
 {
 	const char *test_string = "abcdefghijkl";
@@ -820,6 +863,9 @@ static struct kunit_case string_test_cases[] = {
 	KUNIT_CASE(string_test_strlen_bench),
 #endif
 	KUNIT_CASE(string_test_strnlen),
+#ifdef __HAVE_ARCH_STRNLEN
+	KUNIT_CASE(string_test_strnlen_bench),
+#endif
 	KUNIT_CASE(string_test_strchr),
 	KUNIT_CASE(string_test_strnchr),
 	KUNIT_CASE(string_test_strrchr),
-- 
2.25.1