В Вт, 11/11/2014 в 10:30 +0800, Wanpeng Li пишет:
> 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 fix it by push the task to another cpu in dl_task_timer() if
> rq is offline.
>
> Signed-off-by: Wanpeng Li <wanpeng...@linux.intel.com>
I'm still thinking we don't have to guarantee any "deadlines" during cpu
hotplug...
But, if speaking about this way:
> ---
> 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 | 51
> ++++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 48 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 00324af..e0fbba4 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -487,6 +487,7 @@ 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
> @@ -538,6 +539,46 @@ again:
> update_rq_clock(rq);
> dl_se->dl_throttled = 0;
> dl_se->dl_yielded = 0;
> +
> + /*
> + * So if we find that the rq the task was on is no longer
> + * available, we need to select a new rq.
> + */
> + if (!rq->online) {
> + struct rq *later_rq = NULL;
> +
> + raw_spin_unlock(&rq->lock);
> +
> + later_rq = find_lock_later_rq(p, rq);
find_lock_later_rq() expects that rq is locked.
The comment near its head confuses a reader. It locks newly found rq.
> +
> + if (!later_rq) {
> + int cpu;
> +
> + /*
> + * If cannot preempt any rq, fallback to pick any
> + * online cpu.
> + */
> + for_each_cpu(cpu, tsk_cpus_allowed(p))
> + if (cpu_online(cpu))
> + later_rq = cpu_rq(cpu);
> + if (!later_rq) {
> + pr_warn("fail to find any online and task "
> + "will never come back to us\n");
> + goto out;
> + }
> + }
> +
> + deactivate_task(rq, p, 0);
> + set_task_cpu(p, later_rq->cpu);
> + activate_task(later_rq, p, 0);
> +
> + resched_curr(later_rq);
> +
> + double_unlock_balance(rq, later_rq);
double_unlock_balance() unlocks later_rq only.
> +
> + goto out;
> + }
> +
> if (task_on_rq_queued(p)) {
> enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);
> if (dl_task(rq->curr))
> @@ -555,7 +596,7 @@ again:
> }
> unlock:
> raw_spin_unlock(&rq->lock);
> -
> +out:
> return HRTIMER_NORESTART;
> }
>
> @@ -1185,8 +1226,12 @@ static int find_later_rq(struct task_struct *task)
> * We have to consider system topology and task affinity
> * first, then we can look for a suitable cpu.
> */
> - cpumask_copy(later_mask, task_rq(task)->rd->span);
> - cpumask_and(later_mask, later_mask, cpu_active_mask);
> + if (likely(task_rq(task)->online)) {
> + cpumask_copy(later_mask, task_rq(task)->rd->span);
> + cpumask_and(later_mask, later_mask, cpu_active_mask);
> + } else
> + /* for offline cpus we have a singleton rd */
> + cpumask_copy(later_mask, cpu_active_mask);
> cpumask_and(later_mask, later_mask, &task->cpus_allowed);
> best_cpu = cpudl_find(&task_rq(task)->rd->cpudl,
> task, later_mask);
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