Hi Ilpo,
On 10/4/24 7:20 AM, Ilpo Järvinen wrote:
On Thu, 12 Sep 2024, Reinette Chatre wrote:
By default the MBM and MBA tests use the "fill_buf" benchmark to read from a buffer with the goal to measure the memory bandwidth generated by this buffer access.
Care should be taken when sizing the buffer used by the "fill_buf" benchmark. If the buffer is small enough to fit in the cache then it cannot be expected that the benchmark will generate much memory bandwidth. For example, on a system with 320MB L3 cache the existing hardcoded default of 250MB is insufficient.
Use the measured cache size to determine a buffer size that can be expected to trigger memory access while keeping the existing default as minimum that has been appropriate for testing so far.
Signed-off-by: Reinette Chatre reinette.chatre@intel.com
Changes since V1:
- Ensure buffer is at least double L3 cache size. (Ilpo)
- Support user override of default buffer size. (Ilpo)
tools/testing/selftests/resctrl/mba_test.c | 8 +++++++- tools/testing/selftests/resctrl/mbm_test.c | 8 +++++++- 2 files changed, 14 insertions(+), 2 deletions(-)
diff --git a/tools/testing/selftests/resctrl/mba_test.c b/tools/testing/selftests/resctrl/mba_test.c index 7e43056c8737..d8d9637c1951 100644 --- a/tools/testing/selftests/resctrl/mba_test.c +++ b/tools/testing/selftests/resctrl/mba_test.c @@ -182,7 +182,13 @@ static int mba_run_test(const struct resctrl_test *test, const struct user_param fill_buf.memflush = uparams->fill_buf->memflush; param.fill_buf = &fill_buf; } else if (!uparams->benchmark_cmd[0]) {
fill_buf.buf_size = DEFAULT_SPAN;
unsigned long cache_total_size = 0;ret = get_cache_size(uparams->cpu, "L3", &cache_total_size);if (ret)return ret;fill_buf.buf_size = cache_total_size * 2 > DEFAULT_SPAN ?cache_total_size * 2 : DEFAULT_SPAN;diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c index b1f03a73333f..7635ee6b9339 100644 --- a/tools/testing/selftests/resctrl/mbm_test.c +++ b/tools/testing/selftests/resctrl/mbm_test.c @@ -149,7 +149,13 @@ static int mbm_run_test(const struct resctrl_test *test, const struct user_param fill_buf.memflush = uparams->fill_buf->memflush; param.fill_buf = &fill_buf; } else if (!uparams->benchmark_cmd[0]) {
fill_buf.buf_size = DEFAULT_SPAN;
unsigned long cache_total_size = 0;ret = get_cache_size(uparams->cpu, "L3", &cache_total_size);if (ret)return ret;fill_buf.buf_size = cache_total_size * 2 > DEFAULT_SPAN ?cache_total_size * 2 : DEFAULT_SPAN;It has a bit of code duplication feel in it so I'd consider adding something like ssize_t get_default_span() (perhaps there exists a better name for it that is not "span" based). Also DEFAULT_SPAN is no longer truly the default span.
Good suggestion. How about get_fill_buf_size()?
Regarding the "DEFAULT_SPAN" it seems to have some 'magic number smell' to it. When I tried to eliminate it and only rely on cache size the tests were failing on some earlier platforms with smaller L3. I then started treating it as a minimum in order to keep original behavior on these earlier systems. Perhaps renaming it to "MINIMUM_SPAN" would make this change clear?
But neither is the end of the world as is...
Reviewed-by: Ilpo Järvinen ilpo.jarvinen@linux.intel.com
Thank you very much.
Reinette