sched/fair: Add per-CPU min capacity to sched_group_capacity

struct sched_group_capacity currently represents the compute capacity
sum of all CPUs in the sched_group.

Unless it is divided by the group_weight to get the average capacity
per CPU, it hides differences in CPU capacity for mixed capacity systems
(e.g. high RT/IRQ utilization or ARM big.LITTLE).

But even the average may not be sufficient if the group covers CPUs of
different capacities.

Instead, by extending struct sched_group_capacity to indicate min per-CPU
capacity in the group a suitable group for a given task utilization can
more easily be found such that CPUs with reduced capacity can be avoided
for tasks with high utilization (not implemented by this patch).

Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dietmar.eggemann@arm.com
Cc: freedom.tan@mediatek.com
Cc: keita.kobayashi.ym@renesas.com
Cc: mgalbraith@suse.de
Cc: sgurrappadi@nvidia.com
Cc: vincent.guittot@linaro.org
Cc: yuyang.du@intel.com
Link: http://lkml.kernel.org/r/1476452472-24740-4-git-send-email-morten.rasmussen@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 055f935d4421..345c1ccaba34 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -892,7 +892,8 @@ struct sched_group_capacity {
 	 * CPU capacity of this group, SCHED_CAPACITY_SCALE being max capacity
 	 * for a single CPU.
 	 */
-	unsigned int capacity;
+	unsigned long capacity;
+	unsigned long min_capacity; /* Min per-CPU capacity in group */
 	unsigned long next_update;
 	int imbalance; /* XXX unrelated to capacity but shared group state */