Re: [PATCH 2/2] sched/deadline: fix start high-res preemption tick for a non-running task
From: Juri Lelli
Date: Mon Nov 17 2014 - 04:50:44 EST
On 13/11/14 10:30, Wanpeng Li wrote:
> Hi Juri,
> On 11/13/14, 5:37 PM, Juri Lelli wrote:
>> not sure I understand what the problem is here.
>> On 11/11/14 01:52, Wanpeng Li wrote:
>>> Queued ticks are scheduled to match the budget, which means the budget
>>> is overall consumed and the dl task should be throttled.
>> ... enforce the budget? It means that when the budget is consumed the
>> task has to be throttled...
>>> Dl task will
>>> be replenished immediately if fail to start a dl timer.
>>> However, the curr maybe not the left most dl task in the rb tree any
>>> more after this immediately replenished and reschedule is needed.
>>> Start high-res preemption tick for this upcoming rescheduled dl task
>>> is not correct.
>> So, the task that is going to preempt curr is picked by
>> pick_next_task_dl(), that correctly starts the hrtick for this new task.
>> Maybe you can add more information about what you are seeing? A callpath
> The parameter of task_tick_dl() queued == 1 means that hrtick is fired.
> hrtick() => task_tick_dl( , ,1), so p->dl.runtime should be <= 0 if
> queued == 1. What I see is queued == 1 && p->dl.runtime > 0 && p is not
> the left most task and hrtick is start for this task.
Oh, right, now it makes sense. Good catch! :)
Could you please post a second version with a more explanatory changelog
and maybe a comment just above the check?
> Wanpeng Li
>> - Juri
>>> This patch fix it by not starting high-res preemption tick for a
>>> non-running dl task.
>>> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx>
>>> 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 56674f6..2a6a5bb 100644
>>> --- a/kernel/sched/deadline.c
>>> +++ b/kernel/sched/deadline.c
>>> @@ -1090,7 +1090,8 @@ static void task_tick_dl(struct rq *rq, struct task_struct *p, int queued)
>>> - if (hrtick_enabled(rq) && queued && p->dl.runtime > 0)
>>> + if (hrtick_enabled(rq) && queued && p->dl.runtime > 0 &&
>>> + is_leftmost(p, &rq->dl))
>>> start_hrtick_dl(rq, p);
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