On Thu, 29 Aug 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
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 8ad433495f61..cad473b81a64 100644 --- a/tools/testing/selftests/resctrl/mba_test.c +++ b/tools/testing/selftests/resctrl/mba_test.c @@ -170,11 +170,17 @@ static int mba_run_test(const struct resctrl_test *test, const struct user_param .setup = mba_setup, .measure = mba_measure, };
- unsigned long cache_total_size = 0; int ret;
remove(RESULT_FILE_NAME);
- param.fill_buf.buf_size = DEFAULT_SPAN;
- ret = get_cache_size(uparams->cpu, "L3", &cache_total_size);
- if (ret)
return ret;- param.fill_buf.buf_size = cache_total_size > DEFAULT_SPAN ?
cache_total_size * 2 : DEFAULT_SPAN;
Should the check leave a bit of safeguard so that the buf_size is at least 2x (or x1.25 or some other factor)?
In here buf_size immediate jumps from 1x -> 2x when cache_total_size goes from DEFAULT_SPAN to DEFAULT_SPAN+1 (obviously L3 size won't be odd like that but I think you get my point).
Also, user might want to override this as mentioned in my reply to the previous patch.