linux-kernel - [PATCH v3] sched/fair: use utilization to select misfit task

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Message-Id: <1564750572-20251-1-git-send-email-vincent.guittot@linaro.org>
Date:   Fri,  2 Aug 2019 14:56:12 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org
Cc:     pauld@...hat.com, valentin.schneider@....com,
        srikar@...ux.vnet.ibm.com, quentin.perret@....com,
        dietmar.eggemann@....com, Morten.Rasmussen@....com,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH v3] sched/fair: use utilization to select misfit task

utilization is used to detect a misfit task but the load is then used to
select the task on the CPU which can lead to select a small task with
high weight instead of the task that triggered the misfit migration.

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
Keep tracking load instead of utilization but check that 
task doesn't fit CPU's capacity when selecting the task to detach as
suggested by Valentin 

 kernel/sched/fair.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 53e64a7..8496118 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7487,15 +7487,9 @@ static int detach_tasks(struct lb_env *env)
 			break;
 
 		case migrate_misfit:
-			load = task_h_load(p);
-
-			/*
-			 * utilization of misfit task might decrease a bit
-			 * since it has been recorded. Be conservative in the
-			 * condition.
-			 */
-			if (load < env->imbalance)
-				goto next;
+			/* This is not a misfit task */
+                       if (task_fits_capacity(p, capacity_of(env->src_cpu)))
+			       goto next;
 
 			env->imbalance = 0;
 			break;
-- 
2.7.4