ANDROID: sched/fair: Avoid unnecessary balancing of asymmetric capacity groups

On systems with asymmetric cpu capacities, a skewed load distribution
might yield better throughput than balancing load per group capacity.
For example, running compute intensive tasks on high capacity cpus while
leaving low capacity cpus idle. So we let load-balance back off if the
busiest group isn't really overloaded.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>

Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Change-Id: I8b08a0fa73f357a9972324bc76cec3912fe293cf
Signed-off-by: Chris Redpath <chris.redpath@arm.com>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9cf5d479cbbd12a20965ad61e90a0bbcbed87fd3..509cd715ab81af88f0f402e0b0ba48fcac5b1d98 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7569,6 +7569,15 @@ static bool update_sd_pick_busiest(struct lb_env *env,
            group_smaller_cpu_capacity(sds->local, sg))
                return false;
 
+       /*
+        * Candidate sg doesn't face any severe imbalance issues so
+        * don't disturb unless the groups are of similar capacity
+        * where balancing is more harmless.
+        */
+       if (sgs->group_type == group_other &&
+               !group_similar_cpu_capacity(sds->local, sg))
+               return false;
+
 asym_packing:
        /* This is the busiest node in its class. */
        if (!(env->sd->flags & SD_ASYM_PACKING))