BUG/MEDIUM: cpu-topo: Distribute CPUs fairly across groups

Make sure CPUs are distributed fairly across groups, in case the number
of groups to generate is not a divider of the number of CPUs, otherwise
we may end up with a few groups that will have no CPU bound to them.

This was introduced in 3.4-dev2 with commit 56fd0c1a5c ("MEDIUM: cpu-topo:
Add an optional directive for per-group affinity"). No backport is
needed unless this commit is backported.

diff --git a/src/cpu_topo.c b/src/cpu_topo.c
index 1af2e3520defe5dcaa07a6e41a2d12bb1fe1ec09..28ed76e0c86be90e63b85662bc3ad6f1ca91dcd5 100644 (file)
--- a/src/cpu_topo.c
+++ b/src/cpu_topo.c
@@ -1286,7 +1286,8 @@ cpu_policy_assign_threads(int cpu_count, int thr_count, struct hap_cpuset node_c
        int thr_per_grp;
        int thr;
        int same_core = 0;
-       int cpu_per_group;
+       int cpu_reminder;
+       int grp_generated = 0;
 
        ha_cpuset_zero(&thrset);
        ha_cpuset_assign(&saved_touse_ccx, &touse_ccx);
@@ -1297,7 +1298,8 @@ cpu_policy_assign_threads(int cpu_count, int thr_count, struct hap_cpuset node_c
        nb_grp = (thr_count + global.maxthrpertgroup - 1) / global.maxthrpertgroup;
        if (nb_grp > MAX_TGROUPS - global.nbtgroups)
                nb_grp = MAX_TGROUPS - global.nbtgroups;
-       cpu_per_group = (cpu_count + nb_grp - 1) / nb_grp;
+       cpu_reminder = cpu_count % nb_grp;
+
        thr_per_grp = (thr_count + nb_grp - 1) / nb_grp;
        if (thr_per_grp > global.maxthrpertgroup)
                thr_per_grp = global.maxthrpertgroup;
@@ -1306,6 +1308,7 @@ cpu_policy_assign_threads(int cpu_count, int thr_count, struct hap_cpuset node_c
                struct hap_cpuset group_cpuset;
                struct hap_cpuset current_tsid;
                struct hap_cpuset current_ccx;
+               int cpu_for_group;
 
                ha_cpuset_zero(&group_cpuset);
                ha_cpuset_zero(&current_tsid);
@@ -1318,6 +1321,11 @@ cpu_policy_assign_threads(int cpu_count, int thr_count, struct hap_cpuset node_c
                if (thr_per_grp + global.nbthread > MAX_THREADS)
                        thr_per_grp = MAX_THREADS - global.nbthread;
 
+               cpu_for_group = cpu_count / nb_grp;
+               if (grp_generated < cpu_reminder)
+                       cpu_for_group++;
+               grp_generated++;
+
                if ((cpu_policy_conf.affinity & (CPU_AFFINITY_PER_GROUP | CPU_AFFINITY_PER_GROUP_LOOSE)) == CPU_AFFINITY_PER_GROUP) {
                        int i = 0;
                        int next_ccx;
@@ -1327,7 +1335,7 @@ cpu_policy_assign_threads(int cpu_count, int thr_count, struct hap_cpuset node_c
                         * Try to allocate them from the same CCX, and then
                         * the same TSID
                         */
-                       while (i < cpu_per_group) {
+                       while (i < cpu_for_group) {
                                int next_cpu = 0;
                                int got_cpu;
 
@@ -1336,7 +1344,7 @@ cpu_policy_assign_threads(int cpu_count, int thr_count, struct hap_cpuset node_c
                                if (next_ccx == -1)
                                        break;
 
-                               while (i < cpu_per_group && (got_cpu = find_next_cpu_ccx(next_cpu, next_ccx)) != -1) {
+                               while (i < cpu_for_group && (got_cpu = find_next_cpu_ccx(next_cpu, next_ccx)) != -1) {
                                        int tsid;
                                        int got_cpu_tsid;
                                        int next_cpu_tsid = 0;
@@ -1345,7 +1353,7 @@ cpu_policy_assign_threads(int cpu_count, int thr_count, struct hap_cpuset node_c
                                                continue;
                                        tsid = ha_cpu_topo[got_cpu].ts_id;
 
-                                       while (i < cpu_per_group && (got_cpu_tsid = find_next_cpu_tsid(next_cpu_tsid, tsid)) != -1) {
+                                       while (i < cpu_for_group && (got_cpu_tsid = find_next_cpu_tsid(next_cpu_tsid, tsid)) != -1) {
                                                next_cpu_tsid = got_cpu_tsid + 1;
                                                if (!ha_cpuset_isset(&node_cpu_set, ha_cpu_topo[got_cpu_tsid].idx))
                                                        continue;
@@ -1360,7 +1368,7 @@ cpu_policy_assign_threads(int cpu_count, int thr_count, struct hap_cpuset node_c
                                 * At this point there is nothing left
                                 * for us in that CCX, forget about it.
                                 */
-                               if (i < cpu_per_group)
+                               if (i < cpu_for_group)
                                        ha_cpuset_clr(&saved_touse_ccx, next_ccx);
 
                        }