[PATCH v2] sched/pelt: fix false running accounting
From: Vincent Guittot
Date: Sat Jul 01 2017 - 01:07:01 EST
The running state is a subset of runnable state which means that running
can't be set if runnable (weight) is cleared. There are corner cases
where the current sched_entity has been already dequeued but cfs_rq->curr
has not been updated yet and still points to the dequeued sched_entity.
If ___update_load_avg is called at that time, weight will be 0 and running
will be set which is not possible.
This case happens during pick_next_task_fair() when a cfs_rq becomes idles.
The current sched_entity has been dequeued so se->on_rq is cleared and
cfs_rq->weight is null. But cfs_rq->curr still points to se (it will be
cleared when picking the idle thread). Because the cfs_rq becomes idle,
idle_balance() is called and ends up to call update_blocked_averages()
with these wrong running and runnable states.
Add a test in ___update_load_avg to correct the running state in this case.
Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
kernel/sched/fair.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 008c514..bc36a75 100644
@@ -2968,6 +2968,18 @@ ___update_load_avg(u64 now, int cpu, struct sched_avg *sa,
sa->last_update_time += delta << 10;
+ * running is a subset of runnable (weight) so running can't be set if
+ * runnable is clear. But there are some corner cases where the current
+ * se has been already dequeued but cfs_rq->curr still points to it.
+ * This means that weight will be 0 but not running for a sched_entity
+ * but also for a cfs_rq if the latter becomes idle. As an example,
+ * this happens during idle_balance() which calls
+ * update_blocked_averages()
+ if (!weight)
+ running = 0;
* Now we know we crossed measurement unit boundaries. The *_avg
* accrues by two steps: