sched: Add group_misfit_task load-balance type

To maximize throughput in systems with reduced capacity cpus (e.g.
high RT/IRQ load and/or ARM big.LITTLE) load-balancing has to consider
task and cpu utilization as well as per-cpu compute capacity when
load-balancing in addition to the current average load based
load-balancing policy. Tasks that are scheduled on a reduced capacity
cpu need to be identified and migrated to a higher capacity cpu if
possible.

To implement this additional policy an additional group_type
(load-balance scenario) is added: group_misfit_task. This represents
scenarios where a sched_group has tasks that are not suitable for its
per-cpu capacity. group_misfit_task is only considered if the system is
not overloaded in any other way (group_imbalanced or group_overloaded).

Identifying misfit tasks requires the rq lock to be held. To avoid
taking remote rq locks to examine source sched_groups for misfit tasks,
each cpu is responsible for tracking misfit tasks themselves and update
the rq->misfit_task flag. This means checking task utilization when
tasks are scheduled and on sched_tick.

Change-Id: I092a348ed0ff37eae123f0d8d6dcf1435d51bfb1
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index bcf13796303b..c5d1981d17da 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -561,6 +561,7 @@ struct rq {
 	#define CPU_LOAD_IDX_MAX 5
 	unsigned long cpu_load[CPU_LOAD_IDX_MAX];
 	unsigned long last_load_update_tick;
+	unsigned int misfit_task;
 #ifdef CONFIG_NO_HZ_COMMON
 	u64 nohz_stamp;
 	unsigned long nohz_flags;