12.03.2014, 14:39, "Nicholas Mc Guire" <der.herr@xxxxxxx>:
> On Wed, 12 Mar 2014, Steven Rostedt wrote:
>
>> Peter,
>>
>> I'm going through my inbox (over a year old), and found this patch from
>> Kirill. It looks fine to me. You can apply it with my
>>
>> Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
>>
>> -- Steve
>>
>> [PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT
>>
>> Just switched pinned task is not able to be pushed. If the rq had had
>> several RT tasks before they have already been considered as candidates
>> to be pushed (or pulled).
>>
>> Signed-off-by: Kirill V Tkhai <tkhai@xxxxxxxxx>
>> CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
>> CC: Ingo Molnar <mingo@xxxxxxxxxx>
>> CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>> CC: linux-rt-users <linux-rt-users@xxxxxxxxxxxxxxx>
>> ---
>> kernel/sched/rt.c | 4 ++--
>> 1 files changed, 2 insertions(+), 2 deletions(-)
>> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
>> index 4e8f0f4..5aab032 100644
>> --- a/kernel/sched/rt.c
>> +++ b/kernel/sched/rt.c
>> @@ -1925,9 +1925,9 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
>> */
>> if (p->on_rq && rq->curr != p) {
>> #ifdef CONFIG_SMP
>> - if (rq->rt.overloaded && push_rt_task(rq) &&
>> + if (p->nr_cpus_allowed > 1 && rq->rt.overloaded &&
>> /* Don't resched if we changed runqueues */
>> - rq != task_rq(p))
>> + push_rt_task(rq) && rq != task_rq(p))
>> check_resched = 0;
>> #endif /* CONFIG_SMP */
>> if (check_resched && p->prio < rq->curr->prio)
>
> would there not need to be a check for p->migrate_disable ?
> push_rt_task() is not checking and so a high prio RT task
> preemting a low prio RT task in a migrate_disable() section
> would actually push it off this cpu ? atleast I did not
> find why that would not happen.
Hi, Nicholas!
p is not rq->curr, so its p->migrate_disable state is already updated and
it can't be pushed (nr_cpus_allowed == 1 and it's not pushable).
(If I understand right, that you worry about this).
Kirill
> thx!
> hofrat
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