linux-kernel - [PATCH 1/2] sched: Fix updating rq->max_idle_balance_cost and rq->next_balance in idle

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Date:	Mon, 28 Apr 2014 15:45:54 -0700
From:	Jason Low <jason.low2@...com>
To:	mingo@...nel.org, peterz@...radead.org, jason.low2@...com
Cc:	linux-kernel@...r.kernel.org, daniel.lezcano@...aro.org,
	alex.shi@...aro.org, preeti@...ux.vnet.ibm.com, efault@....de,
	vincent.guittot@...aro.org, morten.rasmussen@....com, aswin@...com
Subject: [PATCH 1/2] sched: Fix updating rq->max_idle_balance_cost and rq->next_balance in idle_balance()

Commit e5fc6611 can potentially cause rq->max_idle_balance_cost to not be
updated, even when load_balance(NEWLY_IDLE) is attempted and the per-sd
max cost value is updated.

Preeti noticed a similar issue with updating rq->next_balance.

In this patch, we fix this by making sure we still check/update those values
even if a task gets enqueued while browsing the domains.

Cc: daniel.lezcano@...aro.org
Cc: alex.shi@...aro.org   
Cc: efault@....de
Cc: vincent.guittot@...aro.org
Cc: morten.rasmussen@....com
Cc: aswin@...com
Cc: mingo@...nel.org
Reviewed-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Signed-off-by: Jason Low <jason.low2@...com>
---
 kernel/sched/fair.c |   16 ++++++++--------
 1 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index af47873..e0f3019 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6658,6 +6658,7 @@ static int idle_balance(struct rq *this_rq)
 	int this_cpu = this_rq->cpu;
 
 	idle_enter_fair(this_rq);
+
 	/*
 	 * We must set idle_stamp _before_ calling idle_balance(), such that we
 	 * measure the duration of idle_balance() as idle time.
@@ -6714,14 +6715,16 @@ static int idle_balance(struct rq *this_rq)
 
 	raw_spin_lock(&this_rq->lock);
 
+	if (curr_cost > this_rq->max_idle_balance_cost)
+		this_rq->max_idle_balance_cost = curr_cost;
+
 	/*
-	 * While browsing the domains, we released the rq lock.
-	 * A task could have be enqueued in the meantime
+	 * While browsing the domains, we released the rq lock, a task could
+	 * have been enqueued in the meantime. Since we're not going idle,
+	 * pretend we pulled a task.
 	 */
-	if (this_rq->cfs.h_nr_running && !pulled_task) {
+	if (this_rq->cfs.h_nr_running && !pulled_task)
 		pulled_task = 1;
-		goto out;
-	}
 
 	if (pulled_task || time_after(jiffies, this_rq->next_balance)) {
 		/*
@@ -6731,9 +6734,6 @@ static int idle_balance(struct rq *this_rq)
 		this_rq->next_balance = next_balance;
 	}
 
-	if (curr_cost > this_rq->max_idle_balance_cost)
-		this_rq->max_idle_balance_cost = curr_cost;
-
 out:
 	/* Is there a task of a high priority class? */
 	if (this_rq->nr_running != this_rq->cfs.h_nr_running)
-- 
1.7.1

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