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Message-Id: <20260113082748.250916-9-jiangfeng@kylinos.cn>
Date: Tue, 13 Jan 2026 16:27:42 +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 08/14] lib/string_kunit: add performance benchmark for strlen()
Introduce a benchmark to compare the architecture-optimized strlen()
implementation against the generic C version (__generic_strlen).
The benchmark uses a table-driven approach to evaluate performance
across different string lengths (short, medium, and long). It employs
ktime_get() for timing and get_random_bytes() followed by null-byte
filtering to generate test data that prevents early termination.
This helps in quantifying the performance gains of architecture-specific
optimizations on various platforms.
Suggested-by: Andy Shevchenko <andy@...nel.org>
Signed-off-by: Feng Jiang <jiangfeng@...inos.cn>
---
lib/tests/string_kunit.c | 117 +++++++++++++++++++++++++++++++++++++++
1 file changed, 117 insertions(+)
diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
index 8eb095404b95..2266954ae5e0 100644
--- a/lib/tests/string_kunit.c
+++ b/lib/tests/string_kunit.c
@@ -20,6 +20,77 @@
#define STRING_TEST_MAX_LEN 128
#define STRING_TEST_MAX_OFFSET 16
+#if defined(__HAVE_ARCH_STRLEN)
+#define STRING_BENCH_ENABLED
+#endif
+
+#ifdef STRING_BENCH_ENABLED
+/* Configuration for string benchmark scenarios */
+struct string_bench_case {
+ const char *name;
+ size_t len;
+ unsigned int iterations;
+};
+
+static const struct string_bench_case bench_cases[] = {
+ {"short", 8, 100000},
+ {"medium", 64, 100000},
+ {"long", 2048, 10000},
+};
+
+/**
+ * get_max_bench_len() - Get the maximum length from benchmark cases
+ * @cases: array of test cases
+ * @count: number of cases
+ */
+static size_t get_max_bench_len(const struct string_bench_case *cases, size_t count)
+{
+ size_t i, max_len = 0;
+
+ for (i = 0; i < count; i++) {
+ if (cases[i].len > max_len)
+ max_len = cases[i].len;
+ }
+
+ return max_len;
+}
+
+/**
+ * get_random_nonzero_bytes() - Fill buffer with random non-null bytes
+ * @buf: buffer to fill
+ * @len: number of bytes to fill
+ */
+static void get_random_nonzero_bytes(void *buf, size_t len)
+{
+ u8 *s = (u8 *)buf;
+
+ get_random_bytes(buf, len);
+
+ /* Replace null bytes to avoid early string termination */
+ for (size_t i = 0; i < len; i++) {
+ if (s[i] == '\0')
+ s[i] = 0x01;
+ }
+}
+
+static void string_bench_report(struct kunit *test, const char *func,
+ const struct string_bench_case *bc,
+ u64 time_arch, u64 time_generic)
+{
+ u64 ratio_int, ratio_frac;
+
+ /* Calculate speedup ratio with 2 decimal places. */
+ ratio_int = div64_u64(time_generic, time_arch);
+ ratio_frac = div64_u64((time_generic % time_arch) * 100, time_arch);
+
+ kunit_info(test, "%s performance (%s, len: %zu, iters: %u):\n",
+ func, bc->name, bc->len, bc->iterations);
+ kunit_info(test, " arch-optimized: %llu ns\n", time_arch);
+ kunit_info(test, " generic C: %llu ns\n", time_generic);
+ kunit_info(test, " speedup: %llu.%02llux\n", ratio_int, ratio_frac);
+}
+#endif /* STRING_BENCH_ENABLED */
+
static void string_test_memset16(struct kunit *test)
{
unsigned i, j, k;
@@ -129,6 +200,49 @@ static void string_test_strlen(struct kunit *test)
}
}
+#ifdef __HAVE_ARCH_STRLEN
+static void string_test_strlen_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)strlen(buf);
+ }
+ 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_strlen(buf);
+ }
+ end = ktime_get();
+ time_generic = ktime_to_ns(ktime_sub(end, start));
+
+ string_bench_report(test, "strlen", &bench_cases[i],
+ time_arch, time_generic);
+ }
+}
+#endif
+
static void string_test_strnlen(struct kunit *test)
{
char *s;
@@ -702,6 +816,9 @@ static struct kunit_case string_test_cases[] = {
KUNIT_CASE(string_test_memset32),
KUNIT_CASE(string_test_memset64),
KUNIT_CASE(string_test_strlen),
+#ifdef __HAVE_ARCH_STRLEN
+ KUNIT_CASE(string_test_strlen_bench),
+#endif
KUNIT_CASE(string_test_strnlen),
KUNIT_CASE(string_test_strchr),
KUNIT_CASE(string_test_strnchr),
--
2.25.1
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