Hi Juri,
On Mon, Mar 02, 2015 at 12:11:48PM +, Juri Lelli wrote:
>Hi,
>
>On 25/02/2015 11:50, Wanpeng Li wrote:
>> I observe that dl task can't be migrated to other cpus during cpu hotplug,
>> in addition, task may/may not be running again if cpu is added back. The
>> root cause which I found is that dl task will be throtted and removed from
>> dl rq after comsuming all budget, which leads to stop task can't pick it up
>> from dl rq and migrate to other cpus during hotplug.
>>
>> The method to reproduce:
>> schedtool -E -t 5:10 -e ./test
>> Actually test is just a simple for loop. Then observe which cpu the test
>> task is on.
>> echo 0 > /sys/devices/system/cpu/cpuN/online
>>
>> This patch adds the dl task migration during cpu hotplug by finding a most
>> suitable later deadline rq after dl timer fire if current rq is offline,
>> if fail to find a suitable later deadline rq then fallback to any eligible
>> online cpu in order that the deadline task will come back to us, and the
>> push/pull mechanism should then move it around properly.
>>
>> Signed-off-by: Wanpeng Li
>> ---
>> v7 -> v8:
>> * remove rd->span related modification since Pang's commit 16b269436b72
>>(sched/deadline: Modify cpudl::free_cpus to reflect rd->online) merged
>>upstream, which Juri pointed out can handle the exclusive cpusets.
>> * rebase
>> v6 -> v7:
>> * rebase
>> v5 -> v6:
>> * add double_lock_balance in the fallback path
>> v4 -> v5:
>> * remove raw_spin_unlock(&rq->lock)
>> * cleanup codes, spotted by Peterz
>> * cleanup patch description
>> v3 -> v4:
>> * use tsk_cpus_allowed wrapper
>> * fix compile error
>> v2 -> v3:
>> * don't get_task_struct
>> * if cannot preempt any rq, fallback to pick any online cpus
>> * use cpu_active_mask as original later_mask if cpu is offline
>> v1 -> v2:
>> * push the task to another cpu in dl_task_timer() if rq is offline.
>> kernel/sched/deadline.c | 38 ++
>> 1 file changed, 38 insertions(+)
>>
>> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
>> index 3fa8fa6..49f92c8 100644
>> --- a/kernel/sched/deadline.c
>> +++ b/kernel/sched/deadline.c
>> @@ -492,6 +492,7 @@ static int start_dl_timer(struct sched_dl_entity *dl_se,
>> bool boosted)
>> return hrtimer_active(&dl_se->dl_timer);
>> }
>>
>> +static struct rq *find_lock_later_rq(struct task_struct *task, struct rq
>> *rq);
>> /*
>> * This is the bandwidth enforcement timer callback. If here, we know
>> * a task is not on its dl_rq, since the fact that the timer was running
>> @@ -537,6 +538,43 @@ static enum hrtimer_restart dl_task_timer(struct
>> hrtimer *timer)
>> update_rq_clock(rq);
>>
>> /*
>> + * So if we find that the rq the task was on is no longer
>> + * available, we need to select a new rq.
>> + */
>> +if (unlikely(!rq->online)) {
>> +struct rq *later_rq = NULL;
>> +
>> +later_rq = find_lock_later_rq(p, rq);
>> +
>> +if (!later_rq) {
>> +int cpu;
>> +
>> +/*
>> + * If cannot preempt any rq, fallback to pick any
>> + * online cpu.
>> + */
>> +cpu = cpumask_any_and(cpu_active_mask,
>> +tsk_cpus_allowed(p));
>
>Please align this to cpu_active_mask above.
Ok.
>
>> +if (cpu >= nr_cpu_ids) {
>> +pr_warn("fail to find any online cpu and task
>> will never come back\n");
>
>Wouldn't be better a WARN_ON(1) here? It is a pretty
>serious situation.
Good idea.
>
>> +goto unlock;
>> +}
>> +later_rq = cpu_rq(cpu);
>> +double_lock_balance(rq, later_rq);
>> +}
>> +
>> +deactivate_task(rq, p, 0);
>> +set_task_cpu(p, later_rq->cpu);
>> +activate_task(later_rq, p, ENQUEUE_REPLENISH);
>> +
>> +resched_curr(later_rq);
>
>Your later_rq can also come from the cpumask_any_and(), we
>should check if we need a resched here.
I will add the check in next version, great thanks for your review. ;-)
Regards,
Wanpeng Li
>
>Best,
>
>- Juri
>
>> +
>> +double_unlock_balance(rq, later_rq);
>> +
>> +goto unlock;
>> +}
>> +
>> +/*
>> * If the throttle happened during sched-out; like:
>> *
>> * schedule()
>>
--
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