diff mbox

[RFCv5,34/46] sched: Enable idle balance to pull single task towards cpu with higher capacity

Message ID 1436293469-25707-35-git-send-email-morten.rasmussen@arm.com (mailing list archive)
State RFC
Headers show

Commit Message

Morten Rasmussen July 7, 2015, 6:24 p.m. UTC 
From: Dietmar Eggemann <dietmar.eggemann@arm.com>

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 if the
energy aware system operates above the tipping point.

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>
---
 kernel/sched/fair.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

Comments

Peter Zijlstra Aug. 15, 2015, 9:15 a.m. UTC | #1 
On Tue, Jul 07, 2015 at 07:24:17PM +0100, Morten Rasmussen wrote:
> +++ b/kernel/sched/fair.c
> @@ -7569,6 +7569,13 @@ 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);
>  }

Doesn't this allow for a nice game of ping-pong? Where if a task runs on
CPU X and generates interrupts there, its capacity will lower and we'll
migrate it over to CPU Y because that isn't receiving interrupts.

Now the task is running on Y, will generate interrupts there, and sees X
as a more attractive destination.

goto 1
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diff mbox

Patch

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 48ecf02..97eb83e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7569,6 +7569,13 @@  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);
 }
 
@@ -7923,7 +7930,8 @@  static int idle_balance(struct rq *this_rq)
 	this_rq->idle_stamp = rq_clock(this_rq);
 
 	if (this_rq->avg_idle < sysctl_sched_migration_cost ||
-	    !this_rq->rd->overload) {
+	    (!energy_aware() && !this_rq->rd->overload) ||
+	    (energy_aware() && !this_rq->rd->overutilized)) {
 		rcu_read_lock();
 		sd = rcu_dereference_check_sched_domain(this_rq->sd);
 		if (sd)