sched: favour lower logical cpu number for sched_mc balance
Vaidyanathan Srinivasan [Thu, 18 Dec 2008 17:56:16 +0000 (22:56 +0530)]
Impact: change load-balancing direction to match that of irqbalanced

Just in case two groups have identical load, prefer to move load to lower
logical cpu number rather than the present logic of moving to higher logical
number.

find_busiest_group() tries to look for a group_leader that has spare capacity
to take more tasks and freeup an appropriate least loaded group.  Just in case
there is a tie and the load is equal, then the group with higher logical number
is favoured.  This conflicts with user space irqbalance daemon that will move
interrupts to lower logical number if the system utilisation is very low.

Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched.c

index 56b285c..94b9d11 100644 (file)
@@ -3241,7 +3241,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
                 */
                if ((sum_nr_running < min_nr_running) ||
                    (sum_nr_running == min_nr_running &&
-                    cpumask_first(sched_group_cpus(group)) <
+                    cpumask_first(sched_group_cpus(group)) >
                     cpumask_first(sched_group_cpus(group_min)))) {
                        group_min = group;
                        min_nr_running = sum_nr_running;
@@ -3257,7 +3257,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
                if (sum_nr_running <= group_capacity - 1) {
                        if (sum_nr_running > leader_nr_running ||
                            (sum_nr_running == leader_nr_running &&
-                            cpumask_first(sched_group_cpus(group)) >
+                            cpumask_first(sched_group_cpus(group)) <
                             cpumask_first(sched_group_cpus(group_leader)))) {
                                group_leader = group;
                                leader_nr_running = sum_nr_running;