29.09.2014, 19:03, "Juri Lelli" <juri.le...@arm.com>:
> Hi Kirill,
>
> On 27/09/14 09:41, Kirill Tkhai wrote:
>> From: Kirill Tkhai <ktk...@parallels.com>
>>
>> Now rq->curr task can't be dequeued in this function
>> (it's possible only in __schedule()).
>
> Could you please detail about "before", with a reference to the commit
> that made this further change necessary?
I wrote about unlocked context switching, but I've looked one more time
and found that it used to be impossible before too.
We set "rq->curr = next" before prepare_lock_switch(),
so dequeued task wasn't able to be curr.
I'll update both descriptions in v2.
Thanks,
Kirill
>
> Thanks a lot,
>
> - Juri
>> Also, delete "else" branch which is dead code.
>>
>> Signed-off-by: Kirill Tkhai <ktk...@parallels.com>
>> ---
>> kernel/sched/deadline.c | 50
>> +++++++++++++++++++++++------------------------
>> 1 file changed, 24 insertions(+), 26 deletions(-)
>>
>> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
>> index 63f8b4a..38b4f19 100644
>> --- a/kernel/sched/deadline.c
>> +++ b/kernel/sched/deadline.c
>> @@ -1638,35 +1638,33 @@ static void switched_to_dl(struct rq *rq, struct
>> task_struct *p)
>> static void prio_changed_dl(struct rq *rq, struct task_struct *p,
>> int oldprio)
>> {
>> - if (task_on_rq_queued(p) || rq->curr == p) {
>> + if (!task_on_rq_queued(p))
>> + return;
>> #ifdef CONFIG_SMP
>> - /*
>> - * This might be too much, but unfortunately
>> - * we don't have the old deadline value, and
>> - * we can't argue if the task is increasing
>> - * or lowering its prio, so...
>> - */
>> - if (!rq->dl.overloaded)
>> - pull_dl_task(rq);
>> -
>> - /*
>> - * If we now have a earlier deadline task than p,
>> - * then reschedule, provided p is still on this
>> - * runqueue.
>> - */
>> - if (dl_time_before(rq->dl.earliest_dl.curr, p->dl.deadline) &&
>> - rq->curr == p)
>> - resched_curr(rq);
>> -#else
>> - /*
>> - * Again, we don't know if p has a earlier
>> - * or later deadline, so let's blindly set a
>> - * (maybe not needed) rescheduling point.
>> - */
>> + /*
>> + * This might be too much, but unfortunately
>> + * we don't have the old deadline value, and
>> + * we can't argue if the task is increasing
>> + * or lowering its prio, so...
>> + */
>> + if (!rq->dl.overloaded)
>> + pull_dl_task(rq);
>> + /*
>> + * If we now have a earlier deadline task than p,
>> + * then reschedule, provided p is still on this
>> + * runqueue.
>> + */
>> + if (dl_time_before(rq->dl.earliest_dl.curr, p->dl.deadline) &&
>> + rq->curr == p)
>> resched_curr(rq);
>> +#else
>> + /*
>> + * Again, we don't know if p has a earlier
>> + * or later deadline, so let's blindly set a
>> + * (maybe not needed) rescheduling point.
>> + */
>> + resched_curr(rq);
>> #endif /* CONFIG_SMP */
>> - } else
>> - switched_to_dl(rq, p);
>> }
>>
>> const struct sched_class dl_sched_class = {
--
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