Messages in this thread | | | Date | Thu, 5 Mar 2015 18:17:31 +0800 | From | Wanpeng Li <> | Subject | Re: [PATCH v10] sched/deadline: support dl task migration during cpu hotplug |
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Ping Juri, your reviewed-by/acked-by is a great appreciated. ;-) On Thu, Mar 05, 2015 at 10:12:13AM +0800, 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. > >Suggested-by: Juri Lelli <juri.lelli@arm.com> >Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com> >--- >v9 -> v10: > * fix the "WARNING: line over 80 characters" > * handle no admission control >v8 -> v9: > * align tsk_cpus_allowed(p) to cpu_active_mask > * add WARN_ON(1) > * don't resched_curr if later_rq come from the cpumask_any_and() >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 | 54 +++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 54 insertions(+) > >diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c >index 08766a3..1ed6928 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 +538,59 @@ 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; >+ bool fallback = false; >+ >+ later_rq = find_lock_later_rq(p, rq); >+ >+ if (!later_rq) { >+ int cpu; >+ >+ /* >+ * If cannot preempt any rq, fallback to pick any >+ * online cpu. >+ */ >+ fallback = true; >+ cpu = cpumask_any_and(cpu_active_mask, >+ tsk_cpus_allowed(p)); >+ if (cpu >= nr_cpu_ids) { >+ if (dl_bandwidth_enabled()) { >+ /* >+ * Fail to find any suitable cpu. >+ * The task will never come back! >+ */ >+ WARN_ON(1); >+ goto unlock; >+ } else { >+ /* >+ * If admission control is disabled we >+ * try a little harder to let the task >+ * run. >+ */ >+ cpu = cpumask_any(cpu_active_mask); >+ } >+ } >+ 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); >+ >+ if (!fallback) >+ resched_curr(later_rq); >+ >+ double_unlock_balance(rq, later_rq); >+ >+ goto unlock; >+ } >+ >+ /* > * If the throttle happened during sched-out; like: > * > * schedule() >-- >1.9.1
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