From: Dietmar Eggemann <dietmar.eggemann@arm.com>
Date: Mon, 26 Jan 2015 19:47:28 +0000 (+0000)
Subject: sched: Enable idle balance to pull single task towards cpu with higher capacity
X-Git-Tag: firefly_0821_release~176^2~293
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=11d962803d25d080f08f3f3c448fa9e5727694b7;p=firefly-linux-kernel-4.4.55.git

sched: Enable idle balance to pull single task towards cpu with higher capacity

We do not want to miss out on the ability to pull a single remaining
task from a potential source cpu towards an idle destination cpu. Add an
extra criteria to need_active_balance() to kick off active load balance
if the source cpu is over-utilized and has lower capacity than the
destination cpu.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
---

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 60f2e982c6bf..56362ac036b2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4800,6 +4800,11 @@ static inline bool task_fits_spare(struct task_struct *p, int cpu)
 	return __task_fits(p, cpu, cpu_util(cpu));
 }
 
+static bool cpu_overutilized(int cpu)
+{
+	return (capacity_of(cpu) * 1024) < (cpu_util(cpu) * capacity_margin);
+}
+
 /*
  * find_idlest_group finds and returns the least busy CPU group within the
  * domain.
@@ -7016,6 +7021,13 @@ static int need_active_balance(struct lb_env *env)
 			return 1;
 	}
 
+	if ((capacity_of(env->src_cpu) < capacity_of(env->dst_cpu)) &&
+				env->src_rq->cfs.h_nr_running == 1 &&
+				cpu_overutilized(env->src_cpu) &&
+				!cpu_overutilized(env->dst_cpu)) {
+			return 1;
+	}
+
 	return unlikely(sd->nr_balance_failed > sd->cache_nice_tries+2);
 }