[PATCH 1/3] sched: Fix rq->next_balance time going backward

[Tim Chen]

In traces on newidle_balance(), this_rq->next_balance
time goes backward from time to time, e.g.

11.602 (         ): probe:newidle_balance:(ffffffff810d2470) this_rq=0xffff88fe7f8aae00 next_balance=0x1004fb76c jiffies=0x1004fb739
11.624 (         ): probe:newidle_balance:(ffffffff810d2470) this_rq=0xffff88fe7f8aae00 next_balance=0x1004fb731 jiffies=0x1004fb739
13.856 (         ): probe:newidle_balance:(ffffffff810d2470) this_rq=0xffff88fe7f8aae00 next_balance=0x1004fb76c jiffies=0x1004fb73b
13.910 (         ): probe:newidle_balance:(ffffffff810d2470) this_rq=0xffff88fe7f8aae00 next_balance=0x1004fb731 jiffies=0x1004fb73b
14.637 (         ): probe:newidle_balance:(ffffffff810d2470) this_rq=0xffff88fe7f8aae00 next_balance=0x1004fb76c jiffies=0x1004fb73c
14.666 (         ): probe:newidle_balance:(ffffffff810d2470) this_rq=0xffff88fe7f8aae00 next_balance=0x1004fb731 jiffies=0x1004fb73c

This was due to newidle_balance() updated this_rq->next_balance
to an earlier time than its current value. The real intention
was to make sure next_balance move this_rq->next_balance forward
in its update:

out:
	/* Move the next balance forward */
	if (time_after(this_rq->next_balance, next_balance))
		this_rq->next_balance = next_balance;

The actual outcome was moving this_rq->next_balance backward,
in the wrong direction.

Fix the incorrect check on next_balance causing the problem.

Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1d75af1ecfb4..b0b5698b2184 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10681,7 +10681,7 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
 
 out:
 	/* Move the next balance forward */
-	if (time_after(this_rq->next_balance, next_balance))
+	if (time_after(next_balance, this_rq->next_balance))
 		this_rq->next_balance = next_balance;
 
 	if (pulled_task)
-- 
2.20.1