On 01/28/2014 08:26 AM, Kirill Tkhai wrote:
> v2: Changed comment
>
> When p is current and it's not of dl class, then there are no other
> dl taks in the rq. If we had had pushable tasks in some other rq,
^ tasks
> they would have been pushed earlier. So, skip "p == rq->curr" case.
>
> [This is confirmed by Juri Lelli and LKML was CC'ed, but
> unfotunately I can't find direct link on lkml.org]
>
This was the story:
> On 01/08/2014 10:00 AM, Juri Lelli wrote:
>> On 12/18/2013 04:00 PM, Kirill Tkhai wrote:
>>> 17.12.2013, 16:48, "Peter Zijlstra" <pet...@infradead.org>:
>>> From: Dario Faggioli <raist...@linux.it>
>>>
>>> Introduces the data structures, constants and symbols needed for
>>> SCHED_DEADLINE implementation.
>>
>> [snipped]
>>
>>> +static void switched_to_dl(struct rq *rq, struct task_struct *p)
>>> +{
>>> + /*
>>> + * If p is throttled, don't consider the possibility
>>> + * of preempting rq->curr, the check will be done right
>>> + * after its runtime will get replenished.
>>> + */
>>> + if (unlikely(p->dl.dl_throttled))
>>> + return;
>>> +
>>> + if (!p->on_rq || rq->curr != p) {
>>> + if (task_has_dl_policy(rq->curr))
>>> + check_preempt_curr_dl(rq, p, 0);
>>> + else
>>> + resched_task(rq->curr);
>>> + }
>>> +}
>>
>> The second if() looks a little strange. Why is "!p->on_rq ||" here? RT class
>> has another logic.
>>
>
> You are right, good catch! :)
>
> This has to be changed in
>
> if (p->on_rq && rq->curr != p)
>
> as in RT.
>
> Thanks,
>
> - Juri
> Signed-off-by: Kirill Tkhai <ktk...@parallels.com>
> CC: Juri Lelli <juri.le...@gmail.com>
> CC: Peter Zijlstra <pet...@infradead.org>
> CC: Ingo Molnar <mi...@kernel.org>
> ---
> kernel/sched/deadline.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 0de2482..dd19d6d 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1559,7 +1559,7 @@ static void switched_to_dl(struct rq *rq, struct
> task_struct *p)
> if (unlikely(p->dl.dl_throttled))
> return;
>
> - if (p->on_rq || rq->curr != p) {
> + if (p->on_rq && rq->curr != p) {
> #ifdef CONFIG_SMP
> if (rq->dl.overloaded && push_dl_task(rq) && rq != task_rq(p))
> /* Only reschedule if pushing failed */
>
So the patch looks good. Not sure about the changelog, though :).
Thanks,
- Juri
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