sched: Fix updating rq->max_idle_balance_cost and rq->next_balance in idle_balance()

The following commit:

  e5fc66119ec9 ("sched: Fix race in idle_balance()")

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.

Signed-off-by: Jason Low <jason.low2@hp.com>
Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: morten.rasmussen@arm.com
Cc: aswin@hp.com
Cc: daniel.lezcano@linaro.org
Cc: alex.shi@linaro.org
Cc: efault@gmx.de
Cc: vincent.guittot@linaro.org
Link: http://lkml.kernel.org/r/1398725155-7591-2-git-send-email-jason.low2@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 8 insertions, 8 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7570dd969c28..0fdb96de81a5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6653,6 +6653,7 @@ 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.
@@ -6705,14 +6706,16 @@ 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)) {
                 /*
@@ -6722,9 +6725,6 @@ 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 &&