linux-kernel - [RFC 3/3] sched: ignore task_h_load for CPU_NEWLY

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Date:   Mon,  2 Jan 2017 16:39:48 +0100
From:   Uladzislau Rezki <urezki@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Uladzislau 2 Rezki <uladzislau2.rezki@...ymobile.com>
Subject: [RFC 3/3] sched: ignore task_h_load for CPU_NEWLY_IDLE

From: Uladzislau 2 Rezki <uladzislau2.rezki@...ymobile.com>

A load balancer calculates imbalance factor for particular shed
domain and tries to steal up the prescribed amount of weighted load.
However, a small imbalance factor would sometimes prevent us from
stealing any tasks at all. When a CPU is newly idle, it should
steal first task which passes a migration criteria.

Signed-off-by: Uladzislau 2 Rezki <uladzislau2.rezki@...ymobile.com>
---
 kernel/sched/fair.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9ebcab1..00b63cc 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6534,8 +6534,9 @@ static int detach_tasks(struct lb_env *env)
 		if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed)
 			goto next;
 
-		if ((load / 2) > env->imbalance)
-			goto next;
+		if (env->idle != CPU_NEWLY_IDLE)
+			if ((load / 2) > env->imbalance)
+				goto next;
 
 		detach_task(p, env);
 		list_add(&p->se.group_node, &env->tasks);
-- 
2.1.4