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@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; 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. -- i. > 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; >
