[PATCH v2] sched/fair: fix update the nohz.next_balance even if we haven't done any load balance

[Wanpeng Li]

As Srikar pointed out (https://lkml.org/lkml/2015/3/27/26):

| With the current code when the ilb cpus are not free:
| - We would be updating the nohz.next_balance even through we havent done
|   any load balance.
| - We might iterate thro the nohz.idle_cpus_mask()s to find balance_cpus.

This patch fix it by adding need_resched check with the idle check, and
keep the need_resched check in for loop to catch ilb get busy.

Suggested-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Jason Low <jason.low2@xxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@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 0576ce0..788e42f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7638,7 +7638,7 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
 	struct rq *rq;
 	int balance_cpu;
 
-	if (idle != CPU_IDLE ||
+	if (idle != CPU_IDLE || need_resched() ||
 	    !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)))
 		goto end;
 
-- 
1.9.1

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