sched/fair: change migration destination based on CPU utilization

The patch changes 'fitness' of the destination CPU during migration.
The destiation CPU can have lite utilization of around ~6% and
in that case the task utilization is neglected (since the src CPU
is allready overutilized).

Signed-off-by: Lukasz Luba <l.luba@partner.samsung.com>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8ac2ad9a5b8d178959a6bfbbde4a4c45e0316061..d6c9e4b413305c69f72fad416d6491d72829c651 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7616,7 +7616,7 @@ static inline bool check_cpu_spare_capacity(int cpu,
                                          unsigned int needed_spare_capacity)
 {
        return (capacity_of(cpu) >
-               (cpu_util(cpu) + (needed_spare_capacity / 2)));
+               (cpu_util(cpu) + needed_spare_capacity));
 
 }
 
@@ -9105,6 +9105,12 @@ static struct rq *find_busiest_queue(struct lb_env *env,
  */
 #define MAX_PINNED_INTERVAL    512
 
+static inline bool check_cpu_lite_util(int cpu)
+{
+       /* Lite utilization is defined as less then ~6% */
+       return (capacity_of(cpu) >> 4 >= cpu_util(cpu));
+}
+
 static inline int need_park_into_spare_capacity(struct lb_env *env)
 {
        bool fits_in = check_cpu_spare_capacity(env->dst_cpu,
@@ -9115,7 +9121,7 @@ static inline int need_park_into_spare_capacity(struct lb_env *env)
                                env->src_rq->cfs.h_nr_running == 1 &&
                                cpu_overutilized(env->src_cpu) &&
                                !cpu_overutilized(env->dst_cpu) &&
-                               fits_in) {
+                               (fits_in || check_cpu_lite_util(env->dst_cpu))) {
                ret = 1;
        } else {
                ret = 0;