Errata for Sierra Forest [1] (SRF42) and Granite Rapids[2] (GNR12) describe the problem that MBM on Intel RDT may overcount memory bandwidth measurements. The resctrl tests compare memory bandwidth reported by iMC PMU to that reported by MBM causing the tests to fail on these systems depending on the settings of the platform related to the errata.
Since the resctrl tests need to run under various conditions it is not possible to ensure system settings are such that MBM will not overcount. It has been observed that the overcounting can be controlled via the buffer size used in the MBM and MBA tests that rely on comparisons between iMC PMU and MBM measurements. Running the MBM test on affected platforms with different buffer sizes it can be observed that the difference between iMC PMU and MBM counts reduce as the buffer size increases. After increasing the buffer size to more than 4X the differences between iMC PMU and MBM become insignificant. Increase the buffer size used in MBM and MBA tests to 4X L3 size to reduce possibility of tests failing due to difference in counts reported by iMC PMU and MBM. Signed-off-by: Reinette Chatre <[email protected]> Link: https://edc.intel.com/content/www/us/en/design/products-and-solutions/processors-and-chipsets/sierra-forest/xeon-6700-series-processor-with-e-cores-specification-update/errata-details/ # [1] Link: https://edc.intel.com/content/www/us/en/design/products-and-solutions/processors-and-chipsets/birch-stream/xeon-6900-6700-6500-series-processors-with-p-cores-specification-update/011US/errata-details/ # [2] --- tools/testing/selftests/resctrl/fill_buf.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/resctrl/fill_buf.c b/tools/testing/selftests/resctrl/fill_buf.c index 19a01a52dc1a..b9fa7968cd6e 100644 --- a/tools/testing/selftests/resctrl/fill_buf.c +++ b/tools/testing/selftests/resctrl/fill_buf.c @@ -139,6 +139,6 @@ ssize_t get_fill_buf_size(int cpu_no, const char *cache_type) if (ret) return ret; - return cache_total_size * 2 > MINIMUM_SPAN ? - cache_total_size * 2 : MINIMUM_SPAN; + return cache_total_size * 4 > MINIMUM_SPAN ? + cache_total_size * 4 : MINIMUM_SPAN; } -- 2.50.1
