From c3cdcdac39b66d76a637974400f471df2f155949 Mon Sep 17 00:00:00 2001
From: Vincent Guittot <vincent.guittot@linaro.org>
Date: Sat, 1 Jul 2017 07:06:13 +0200
Subject: [PATCH] sched/pelt: Fix false running accounting
References: bnc#1066110 Scheduler utilisation tracking
Patch-mainline: v4.14-rc1
Git-commit: f235a54f00449c611f85173fe8a66c4d189c5ce1
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@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Morten.Rasmussen@arm.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dietmar.eggemann@arm.com
Link: http://lkml.kernel.org/r/1498885573-18984-1-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
kernel/sched/fair.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3ea419d336ef..3c78f14cab60 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3159,6 +3159,18 @@ ___update_load_sum(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: