Messages in this thread Patch in this message | | | From | Vincent Guittot <> | Subject | [PATCH] sched/pelt: fix false running accounting in PELT | Date | Fri, 30 Jun 2017 15:58:38 +0200 |
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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> --- kernel/sched/fair.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 008c514..5fdcb42 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2968,6 +2968,24 @@ ___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 = 1; + + /* + * Scale time to reflect the amount a computation effectively done + * during the time slot at current capacity + */ + delta = scale_time(delta, cpu, sa, weight, running); + + /* * Now we know we crossed measurement unit boundaries. The *_avg * accrues by two steps: * -- 2.7.4
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