From: Xiaochen Shen Date: Wed, 17 Dec 2025 03:04:53 +0000 (+0800) Subject: selftests/resctrl: Fix a division by zero error on Hygon X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=671ef08d9455f5754d1fc96f5a14e357d6b80936;p=thirdparty%2Fkernel%2Flinux.git selftests/resctrl: Fix a division by zero error on Hygon Change to adjust effective L3 cache size with SNC enabled change introduced the snc_nodes_per_l3_cache() function to detect the Intel Sub-NUMA Clustering (SNC) feature by comparing #CPUs in node0 with #CPUs sharing LLC with CPU0. The function was designed to return: (1) >1: SNC mode is enabled. (2) 1: SNC mode is not enabled or not supported. However, on certain Hygon CPUs, #CPUs sharing LLC with CPU0 is actually less than #CPUs in node0. This results in snc_nodes_per_l3_cache() returning 0 (calculated as cache_cpus / node_cpus). This leads to a division by zero error in get_cache_size(): *cache_size /= snc_nodes_per_l3_cache(); Causing the resctrl selftest to fail with: "Floating point exception (core dumped)" Fix the issue by ensuring snc_nodes_per_l3_cache() returns 1 when SNC mode is not supported on the platform. Updated commit log to fix commit has issues: Shuah Khan Link: https://lore.kernel.org/r/20251217030456.3834956-2-shenxiaochen@open-hieco.net Fixes: a1cd99e700ec ("selftests/resctrl: Adjust effective L3 cache size with SNC enabled") Signed-off-by: Xiaochen Shen Reviewed-by: Reinette Chatre Reviewed-by: Fenghua Yu Signed-off-by: Shuah Khan --- diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c index 195f04c4d1586..b9c1bfb6cc029 100644 --- a/tools/testing/selftests/resctrl/resctrlfs.c +++ b/tools/testing/selftests/resctrl/resctrlfs.c @@ -243,6 +243,16 @@ int snc_nodes_per_l3_cache(void) } snc_mode = cache_cpus / node_cpus; + /* + * On some platforms (e.g. Hygon), + * cache_cpus < node_cpus, the calculated snc_mode is 0. + * + * Set snc_mode = 1 to indicate that SNC mode is not + * supported on the platform. + */ + if (!snc_mode) + snc_mode = 1; + if (snc_mode > 1) ksft_print_msg("SNC-%d mode discovered.\n", snc_mode); }