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@xxxxxxxxx> --- 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; param.fill_buf.memflush = 1; param.fill_buf.operation = 0; param.fill_buf.once = false; diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c index b6883f274c74..734bfa4f42b3 100644 --- a/tools/testing/selftests/resctrl/mbm_test.c +++ b/tools/testing/selftests/resctrl/mbm_test.c @@ -138,11 +138,17 @@ static int mbm_run_test(const struct resctrl_test *test, const struct user_param .setup = mbm_setup, .measure = mbm_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; param.fill_buf.memflush = 1; param.fill_buf.operation = 0; param.fill_buf.once = false; -- 2.46.0
