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 50000:100000 -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 <wanpeng...@linux.intel.com>
> ---
> 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.
> + 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.
> + 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.
Best,
- Juri
> +
> + double_unlock_balance(rq, later_rq);
> +
> + goto unlock;
> + }
> +
> + /*
> * If the throttle happened during sched-out; like:
> *
> * schedule()
>
--
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