MINOR: cpu-topo: ignore single-core clusters

Some platforms (several armv7, intel 14900 etc) report one distinct
cluster per core. This is problematic as it cannot let clusters be
used to distinguish real groups of cores, and cannot be used to build
thread groups.

Let's just compare the cluster cpus to the siblings, and ignore it if
they exactly match. We must also take care of not falling back to
core_cpus_list, which can enumerate cores that already have their
cluster assigned (e.g. intel 14900 has 4 4-Ecore clusters in addition
to the 8 Pcores).

diff --git a/src/cpu_topo.c b/src/cpu_topo.c
index b464f09d7a19b2f39331999ba6460dfc6ce769e0..9c405d7864ba3261f5e182e884a733b128fd0b76 100644 (file)
--- a/src/cpu_topo.c
+++ b/src/cpu_topo.c
@@ -445,6 +445,7 @@ int cpu_detect_topology(void)
        /* detect the presence of some kernel-specific fields */
        no_cache = no_topo = no_capa = no_clust = no_pkg = no_freq = no_cppc = -1;
        for (cpu = 0; cpu <= cpu_topo_lastcpu; cpu++) {
+               struct hap_cpuset siblings_list = { };
                struct hap_cpuset cpus_list;
                int next_level = 1; // assume L1 if unknown
                int idx, level;
@@ -525,18 +526,19 @@ int cpu_detect_topology(void)
                 * share the same cores, and also to tell apart cores that
                 * support SMT from those which do not. When mixed, generally
                 * the ones with SMT are big cores and the ones without are the
-                * small ones.
+                * small ones. We also read the entry if the cluster_id is not
+                * known because we'll have to compare both values.
                 */
-               if (ha_cpu_topo[cpu].ts_id < 0 &&
+               if ((ha_cpu_topo[cpu].ts_id < 0 || ha_cpu_topo[cpu].cl_gid < 0) &&
                    read_line_to_trash(NUMA_DETECT_SYSTEM_SYSFS_PATH "/cpu/cpu%d/topology/thread_siblings_list", cpu) >= 0) {
                        parse_cpu_set_args[0] = trash.area;
                        parse_cpu_set_args[1] = "\0";
-                       if (parse_cpu_set(parse_cpu_set_args, &cpus_list, NULL) == 0) {
+                       if (parse_cpu_set(parse_cpu_set_args, &siblings_list, NULL) == 0) {
                                int sib_id = 0;
 
-                               cpu_id.th_cnt = ha_cpuset_count(&cpus_list);
+                               cpu_id.th_cnt = ha_cpuset_count(&siblings_list);
                                for (cpu2 = 0; cpu2 <= cpu_topo_lastcpu; cpu2++) {
-                                       if (ha_cpuset_isset(&cpus_list, cpu2)) {
+                                       if (ha_cpuset_isset(&siblings_list, cpu2)) {
                                                ha_cpu_topo[cpu2].ts_id  = cpu_id.ts_id;
                                                ha_cpu_topo[cpu2].th_cnt = cpu_id.th_cnt;
                                                ha_cpu_topo[cpu2].th_id  = sib_id++;
@@ -552,6 +554,9 @@ int cpu_detect_topology(void)
                 * above as a fallback for package but we don't care here. We
                 * only consider these values if there's more than one CPU per
                 * cluster (some kernels such as 6.1 report one cluster per CPU).
+                * Note that we purposely ignore clusters that are reportedly
+                * equal to the siblings list, because some machines report one
+                * distinct cluster per *core* (e.g. some armv7 and intel 14900).
                 */
                if (no_clust < 0) {
                        no_clust = !is_file_present(NUMA_DETECT_SYSTEM_SYSFS_PATH "/cpu/cpu%d/topology/cluster_cpus_list", cpu) &&
@@ -563,7 +568,8 @@ int cpu_detect_topology(void)
                     read_line_to_trash(NUMA_DETECT_SYSTEM_SYSFS_PATH "/cpu/cpu%d/topology/core_siblings_list", cpu) >= 0)) {
                        parse_cpu_set_args[0] = trash.area;
                        parse_cpu_set_args[1] = "\0";
-                       if (parse_cpu_set(parse_cpu_set_args, &cpus_list, NULL) == 0 && ha_cpuset_count(&cpus_list) > 1) {
+                       if (parse_cpu_set(parse_cpu_set_args, &cpus_list, NULL) == 0 && ha_cpuset_count(&cpus_list) > 1 &&
+                           (memcmp(&cpus_list, &siblings_list, sizeof(cpus_list)) != 0)) {
                                for (cpu2 = 0; cpu2 <= cpu_topo_lastcpu; cpu2++) {
                                        if (ha_cpuset_isset(&cpus_list, cpu2)) {
                                                ha_cpu_topo[cpu2].cl_lid = cpu_id.cl_lid;