Author: Vincent Guittot <vincent.guit...@linaro.org>
AuthorDate: Sat, 1 Jul 2017 07:06:13 +0200
Committer: Ingo Molnar <mi...@kernel.org>
CommitDate: Thu, 10 Aug 2017 12:18:15 +0200
sched/pelt: Fix false running accounting
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.guit...@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Signed-off-by: Ingo Molnar <mi...@kernel.org>
kernel/sched/fair.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 75c58c7..ef5b66b 100644
@@ -2991,6 +2991,18 @@ ___update_load_avg(u64 now, int cpu, struct sched_avg
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: