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() > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/