Messages in this thread Patch in this message | | | Date | Wed, 19 Feb 2014 11:32:41 +0100 | From | Juri Lelli <> | Subject | Re: [PATCH v3] sched/deadline: Fix bad accounting of nr_running |
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On 02/19/2014 09:46 AM, Peter Zijlstra wrote: > On Tue, Feb 18, 2014 at 09:50:12PM -0500, Steven Rostedt wrote: >> >>> Rationale for this odd behavior is that, when a task is throttled, it >>> is removed only from the dl_rq, but we keep it on_rq (as this is not >>> a "full dequeue", that is the task is not actually sleeping). But, it >>> is also true that, while throttled a task behaves like it is sleeping >>> (e.g., its timer will fire on a new CPU if the old one is dead). So, >>> Steven's fix sounds also semantically correct. >> >> Actually, it seems that I was hitting it again, but this time getting a >> negative number. OK, after looking at the code a bit more, I think we >> should update the runqueue nr_running only when the task is officially >> enqueued and dequeued, and all accounting within, will not touch that >> number.
This is a different way to get the same result (mildly tested on my box):
--- kernel/sched/deadline.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 0dd5e09..675dad3 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -837,7 +837,8 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags) if (!task_current(rq, p) && p->nr_cpus_allowed > 1) enqueue_pushable_dl_task(rq, p);
- inc_nr_running(rq); + if (!(flags & ENQUEUE_REPLENISH)) + inc_nr_running(rq); }
static void __dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags) -- We touch nr_running only when we don't enqueue back as a consequence of a replenishment.
> > But if the task is throttled it should still very much decrement the > number. There's places that very much rely on nr_running be exactly the > number of runnable tasks. >
This is a different thing, and V2 seemed to implement this behavior (that's why I said it looked semantically correct).
Thanks,
- Juri
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