On 2026/1/23 19:02, Andy Shevchenko wrote:
> On Fri, Jan 23, 2026 at 04:58:37PM +0800, Feng Jiang wrote:
>> Introduce a benchmarking framework to the string_kunit test suite to
>> measure the execution efficiency of string functions.
>>
>> The implementation is inspired by crc_benchmark(), measuring throughput
>> (MB/s) and latency (ns/call) across a range of string lengths. It
>> includes a warm-up phase, disables preemption during measurement, and
>> uses a fixed seed for reproducible results.
>>
>> This framework allows for comparing different implementations (e.g.,
>> generic C vs. architecture-optimized assembly) within the KUnit
>> environment.
>>
>> Initially, provide a benchmark for strlen().
>
> ...
>
>> +static void *alloc_max_bench_buffer(struct kunit *test,
>> + const size_t *lens, size_t count, size_t *buf_len)
>> +{
>> + size_t i, max_len = 0;
>> + void *buf;
>
>> + for (i = 0; i < count; i++) {
>> + if (max_len < lens[i])
>> + max_len = lens[i];
>> + }
>
> size_t max_len = 0;
> void *buf;
>
> for (size_t i = 0; i < count; i++)
> max_len = max(lens[i], max_len);
>
Agreed. I will simplify the loop and use max() as suggested.
>> + /* Add space for NUL character */
>> + max_len += 1;
>> +
>> + buf = kunit_kzalloc(test, max_len, GFP_KERNEL);
>> + if (!buf)
>> + return NULL;
>> +
>> + if (buf_len)
>> + *buf_len = max_len;
>> +
>> + return buf;
>> +}
>
> ...
>
>> +#define STRING_BENCH(iters, func, ...)
>> \
>> +({ \
>> + /* Volatile function pointer prevents dead code elimination */ \
>> + typeof(func) (* volatile __func) = (func); \
>> + size_t __bn_iters = (iters); \
>> + size_t __bn_warm_iters; \
>
>> + size_t __bn_i; \
>
> Define it inside for-loop:s.
>
Will do.
>> + u64 __bn_t; \
>> + \
>> + __bn_warm_iters = max(__bn_iters / 10, 50U); \
>> + \
>> + for (__bn_i = 0; __bn_i < __bn_warm_iters; __bn_i++) \
>> + (void)__func(__VA_ARGS__); \
>> + \
>> + preempt_disable(); \
>> + __bn_t = ktime_get_ns(); \
>> + for (__bn_i = 0; __bn_i < __bn_iters; __bn_i++) \
>> + (void)__func(__VA_ARGS__); \
>> + __bn_t = ktime_get_ns() - __bn_t; \
>> + preempt_enable(); \
>> + __bn_t; \
>> +})
>
> ...
>
>> +#define STRING_BENCH_BUF(test, buf_name, buf_size, func, ...)
>> \
>> +do {
>> \
>> + size_t buf_size, _bn_i, _bn_iters, _bn_size = 0; \
>> + u64 _bn_t, _bn_mbps = 0, _bn_lat = 0; \
>> + char *buf_name, *_bn_buf; \
>
>> + if (!IS_ENABLED(CONFIG_STRING_KUNIT_BENCH)) \
>> + kunit_skip(test, "not enabled"); \
>
> Hmm... Since it's a macro anyway, I think the old style is okay:
> >
> #if IS_ENABLED(CONFIG_STRING_KUNIT_BENCH)
> #define STRING_BENCH_BUF(test, buf_name, buf_size, func, ...) \
> ...
> #else
> #define STRING_BENCH_BUF(test, buf_name, buf_size, func, ...) \
> kunit_skip(test, "not enabled"); \
> #endif
>
> But check it that it doesn't produce warnings in `make W=1` case.
>
Thanks. Using #if IS_ENABLED(...) to define the macro differently is cleaner.
I will implement it this way and ensure it passes make W=1 without warnings
>> + _bn_buf = alloc_max_bench_buffer(test, bench_lens, \
>> + ARRAY_SIZE(bench_lens), &_bn_size); \
>> + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, _bn_buf); \
>> + \
>> + fill_random_string(_bn_buf, _bn_size); \
>> + \
>> + for (_bn_i = 0; _bn_i < ARRAY_SIZE(bench_lens); _bn_i++) { \
>> + buf_size = bench_lens[_bn_i]; \
>> + buf_name = _bn_buf + _bn_size - buf_size - 1; \
>> + _bn_iters = STRING_BENCH_WORKLOAD / max(buf_size, 1U); \
>> + \
>> + _bn_t = STRING_BENCH(_bn_iters, func, ##__VA_ARGS__); \
>> + \
>> + if (_bn_t > 0) { \
>> + _bn_mbps = (u64)(buf_size) * _bn_iters * 1000; \
>
> "KILO"? Or "(MEGA/KILO)"? I'm puzzled with this 1000 multiplier.
>
The 1000 factor converts bytes/ns to MB/s：
(bytes/ns) * (10^9 ns/s) / (10^6 bytes/MB)
In v5, I will replace it with (NSEC_PER_SEC / MEGA) to make the unit
conversion explicit and avoid confusion.
>> + _bn_mbps = div64_u64(_bn_mbps, _bn_t); \
>> + _bn_lat = div64_u64(_bn_t, _bn_iters); \
>> + } \
>> + kunit_info(test, "len=%zu: %llu MB/s (%llu ns/call)\n", \
>> + buf_size, _bn_mbps, _bn_lat); \
>> + } \
>> +} while (0)
>
Thanks again for your time and for the detailed review!
--
With Best Regards,
Feng Jiang
