On Thu, May 14, 2026 at 02:13:58PM +0200, Milan Tripkovic wrote:
> From: Milan Tripkovic <[email protected]>
>
> Extend the string benchmarking suite to include memcmp().
> Extend the string unit test to include memcmp().
>
> Reported-by: kernel test robot <[email protected]>
> Closes:
> https://lore.kernel.org/oe-kbuild-all/[email protected]/
> Signed-off-by: Milan Tripkovic <[email protected]>
> ---
> lib/tests/string_kunit.c | 106 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 106 insertions(+)
>
> diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
> index 0819ace5b027..d0bad40a719a 100644
> --- a/lib/tests/string_kunit.c
> +++ b/lib/tests/string_kunit.c
> @@ -881,6 +881,110 @@ static void string_bench_strrchr(struct kunit *test)
> STRING_BENCH_BUF(test, buf, len, strrchr, buf, '\0');
> }
>
> +static void string_test_memcmp(struct kunit *test)
> +{
> + const int max_offset = 16;
> + const int max_len = 32;
> + const int buf_size = max_offset + max_len + 32;
> + u8 *buf1, *buf2;
> + int i, j, len, k;
> +
> + buf1 = kunit_kzalloc(test, buf_size, GFP_KERNEL);
> + buf2 = kunit_kzalloc(test, buf_size, GFP_KERNEL);
> + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buf1);
> + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buf2);
> +
> + for (i = 0; i < max_offset; i++) {
> + for (j = 0; j < max_offset; j++) {
> + for (len = 0; len <= max_len; len++) {
> + memset(buf1, 'A', buf_size);
> + memset(buf2, 'A', buf_size);
> + KUNIT_EXPECT_EQ_MSG(test, memcmp(buf1 + i, buf2
> + j, len), 0,
> + "Should be equal: i:%d j:%d
> len:%d", i, j, len);
> + for (k = 0; k < len; k++) {
> + memset(buf1, 'A', buf_size);
> + memset(buf2, 'A', buf_size);
> + buf2[j + k] = 'B';
> + int res = memcmp(buf1 + i, buf2 + j,
> len);
> +
> + KUNIT_EXPECT_NE_MSG(test, res, 0,
> + "Should detect
> difference at k:%d (i:%d j:%d len:%d)",
> + k, i, j, len);
> +
> + if (buf1[i + k] < buf2[j + k])
> + KUNIT_EXPECT_LT(test, res, 0);
> + else
> + KUNIT_EXPECT_GT(test, res, 0);
> + }
> + }
> + }
> + }
> +}
This looks good, thanks!
> +#if IS_ENABLED(CONFIG_STRING_KUNIT_BENCH)
> +static void string_bench_memcmp(struct kunit *test)
> +{
> + char *buf1, *buf2;
> + size_t lengths[] = { 1, 7, 8, 16, 32, 64, 128, 512, 1024, 4096};
> + int offsets[] = {0, 1, 3, 7};
> + const size_t max_len = 4096 + 64;
I think I'd prefer, instead of a ifdef stub, to do:
if (!IS_ENABLED(CONFIG_STRING_KUNIT_BENCH))
kunit_skip(test, "CONFIG_STRING_KUNIT_BENCH not enabled")
here.
> +
> + buf1 = vmalloc(max_len);
> + buf2 = vmalloc(max_len);
> +
> + if (!buf1 || !buf2) {
> + vfree(buf1);
> + vfree(buf2);
> + kunit_err(test, "vmalloc failed\n");
> + return;
> + }
> +
> + memset(buf1, 'A', max_len);
> + memset(buf2, 'A', max_len);
> +
> + for (int i = 0; i < 100000; i++)
> + (void)memcmp(buf1, buf2, 4096);
> +
> + for (int o = 0; o < ARRAY_SIZE(offsets); o++) {
> + int off = offsets[o];
> +
> + for (int i = 0; i < ARRAY_SIZE(lengths); i++) {
> + size_t len = lengths[i];
> + char *p1 = buf1;
> + char *p2 = buf2 + off;
> +
> + u32 iterations = (len < 512) ? 100000 : 10000;
> +
> + for (u32 j = 0; j < iterations; j++) {
> + (void)memcmp(p1, p2, len);
> + barrier();
> + }
> +
> + u64 elapsed = STRING_BENCH(iterations, memcmp, p1, p2,
> len);
> + u64 ns_per_call = div_u64(elapsed, iterations);
> + u64 mbps = len ? div_u64((u64)len * iterations * 1000,
> +
> elapsed) : 0;
> +
> + if (off == 0) {
> + kunit_info(test, "bench_memcmp_aligned:
> len=%-4zu: %llu MB/s (%llu ns/call)\n",
> + len, mbps, ns_per_call);
> + } else {
> + kunit_info(test,
> "bench_memcmp_unaligned(off=%d): len=%-4zu: %llu MB/s (%llu ns/call)\n",
> + off, len, mbps, ns_per_call);
> + }
> + }
> + }
> +
> + vfree(buf1);
> + vfree(buf2);
> +}
> +#else
> +static void string_bench_memcmp(struct kunit *test)
> +{
> + kunit_skip(test, "not enabled");
> +}
> +#endif
> +
> static struct kunit_case string_test_cases[] = {
> KUNIT_CASE(string_test_memset16),
> KUNIT_CASE(string_test_memset32),
> @@ -910,6 +1014,8 @@ static struct kunit_case string_test_cases[] = {
> KUNIT_CASE(string_bench_strnlen),
> KUNIT_CASE(string_bench_strchr),
> KUNIT_CASE(string_bench_strrchr),
> + KUNIT_CASE(string_test_memcmp),
> + KUNIT_CASE_SLOW(string_bench_memcmp),
> {}
> };
>
> --
> 2.43.0
>
--
Kees Cook
