linux-kernel - [PATCH v2 11/14] lib/string_kunit: add performance benchmark for strrchr()

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Message-Id: <20260113082748.250916-12-jiangfeng@kylinos.cn>
Date: Tue, 13 Jan 2026 16:27:45 +0800
From: Feng Jiang <jiangfeng@...inos.cn>
To: pjw@...nel.org,
	palmer@...belt.com,
	aou@...s.berkeley.edu,
	alex@...ti.fr,
	kees@...nel.org,
	andy@...nel.org,
	akpm@...ux-foundation.org,
	jiangfeng@...inos.cn,
	ebiggers@...nel.org,
	martin.petersen@...cle.com,
	ardb@...nel.org,
	ajones@...tanamicro.com,
	conor.dooley@...rochip.com,
	samuel.holland@...ive.com,
	linus.walleij@...aro.org,
	nathan@...nel.org
Cc: linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH v2 11/14] lib/string_kunit: add performance benchmark for strrchr()

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

Suggested-by: Andy Shevchenko <andy@...nel.org>
Signed-off-by: Feng Jiang <jiangfeng@...inos.cn>
---
 lib/tests/string_kunit.c | 50 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 49 insertions(+), 1 deletion(-)

diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
index e8d527336030..89b583cec2c8 100644
--- a/lib/tests/string_kunit.c
+++ b/lib/tests/string_kunit.c
@@ -21,7 +21,7 @@
 #define STRING_TEST_MAX_OFFSET	16
 
 #if defined(__HAVE_ARCH_STRLEN) || defined(__HAVE_ARCH_STRNLEN) || \
-	defined(__HAVE_ARCH_STRCHR)
+	defined(__HAVE_ARCH_STRCHR) || defined(__HAVE_ARCH_STRRCHR)
 #define STRING_BENCH_ENABLED
 #endif
 
@@ -444,6 +444,51 @@ static void string_test_strnchr(struct kunit *test)
 	KUNIT_ASSERT_NULL(test, result);
 }
 
+#ifdef __HAVE_ARCH_STRRCHR
+static void string_test_strrchr_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);
+		if (bench_cases[i].len > 0)
+			buf[bench_cases[i].len - 1] = 'A';
+		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)strrchr(buf, 'A');
+		}
+		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_strrchr(buf, 'A');
+		}
+		end = ktime_get();
+		time_generic = ktime_to_ns(ktime_sub(end, start));
+
+		string_bench_report(test, "strrchr", &bench_cases[i],
+				time_arch, time_generic);
+	}
+}
+#endif
+
 static void string_test_strspn(struct kunit *test)
 {
 	static const struct strspn_test {
@@ -916,6 +961,9 @@ static struct kunit_case string_test_cases[] = {
 #endif
 	KUNIT_CASE(string_test_strnchr),
 	KUNIT_CASE(string_test_strrchr),
+#ifdef __HAVE_ARCH_STRRCHR
+	KUNIT_CASE(string_test_strrchr_bench),
+#endif
 	KUNIT_CASE(string_test_strspn),
 	KUNIT_CASE(string_test_strcmp),
 	KUNIT_CASE(string_test_strcmp_long_strings),
-- 
2.25.1