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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 >> --- >> 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). Good catch. Will fix. > > Also, user might want to override this as mentioned in my reply to the > previous patch. > ack. Reinette