From: Juri Lelli <juri.lelli@arm.com>
To: Wanpeng Li <wanpeng.li@linux.intel.com>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>
Cc: Kirill Tkhai <ktkhai@parallels.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v5] sched/deadline: support dl task migration during cpu hotplug
Date: Wed, 12 Nov 2014 15:08:44 +0000 [thread overview]
Message-ID: <546377FC.4090408@arm.com> (raw)
In-Reply-To: <1415754413-13988-1-git-send-email-wanpeng.li@linux.intel.com>
Hi,
On 12/11/14 01:06, 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.li@linux.intel.com>
> ---
> 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 | 43 +++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 41 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index f3d7776..7c31906 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 +539,43 @@ 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 (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));
> + if (cpu >= nr_cpu_ids) {
> + pr_warn("fail to find any online cpu and task will never come back\n");
> + goto unlock;
> + }
> + later_rq = cpu_rq(cpu);
> + }
> +
> + 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);
> +
> + goto unlock;
> + }
> +
> if (task_on_rq_queued(p)) {
> enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);
> if (dl_task(rq->curr))
> @@ -1185,8 +1223,9 @@ 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);
> + cpumask_copy(later_mask, cpu_active_mask);
> + if (likely(task_rq(task)->online))
> + cpumask_and(later_mask, later_mask, task_rq(task)->rd->span);
So, here you consider the span only when the task_rq is online,
but there might be others cpus still online belonging to the same
rd->span. And you have to consider them when migrating. Actually,
migration must still be restricted to the online cpus of task's
original rd->span, or I fear you can break clustered scheduling.
Thanks,
- Juri
> cpumask_and(later_mask, later_mask, &task->cpus_allowed);
> best_cpu = cpudl_find(&task_rq(task)->rd->cpudl,
> task, later_mask);
>
next prev parent reply other threads:[~2014-11-12 15:08 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-12 1:06 [PATCH v5] sched/deadline: support dl task migration during cpu hotplug Wanpeng Li
2014-11-12 15:08 ` Juri Lelli [this message]
2014-11-12 15:39 ` Peter Zijlstra
2014-11-12 23:02 ` Wanpeng Li
2015-01-05 14:52 ` Peter Zijlstra
2015-01-06 2:14 ` Wanpeng Li
2014-11-12 23:22 ` Wanpeng Li
2014-11-18 23:18 ` Wanpeng Li
2014-11-19 10:13 ` Juri Lelli
2014-11-19 12:30 ` Wanpeng Li
2014-11-19 13:49 ` Juri Lelli
2014-11-19 23:08 ` Wanpeng Li
2014-11-12 16:27 ` Kirill Tkhai
2014-11-12 22:56 ` Wanpeng Li
2014-11-13 10:10 ` Kirill Tkhai
2014-11-13 10:19 ` Wanpeng Li
2014-11-13 10:21 ` Kirill Tkhai
2014-11-16 22:59 ` Wanpeng Li
2014-11-20 8:49 ` Wanpeng Li
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