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Date: Thu, 5 Mar 2015 09:45:21 +0800
From: Wanpeng Li <wanpeng.li@...ux.intel.com>
To: Juri Lelli <juri.lelli@....com>
Cc: Wanpeng Li <wanpeng.li@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9] sched/deadline: support dl task migration during cpu
hotplug
Hi Juri,
On Wed, Mar 04, 2015 at 09:53:19AM +0000, Juri Lelli wrote:
>Hi,
>
>I think we are still missing a corner case: no admission control, a task
>with an affinity mask of a single cpu, the cpu goes off. In this case we
>could try to let it run just somewhere else, as we don't guarantee anything
>from start. This applies on top of your patch, comments?
>
>Thanks,
>
>- Juri
>
>---
> kernel/sched/deadline.c | 20 +++++++++++++++++---
> 1 file changed, 17 insertions(+), 3 deletions(-)
>
>diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
>index 467ec5d..8dec157 100644
>--- a/kernel/sched/deadline.c
>+++ b/kernel/sched/deadline.c
>@@ -579,10 +579,24 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
> * online cpu.
> */
> fallback = true;
>- cpu = cpumask_any_and(cpu_active_mask, tsk_cpus_allowed(p));
>+ cpu = cpumask_any_and(cpu_active_mask,
>+ tsk_cpus_allowed(p));
Indeed, otherwise "WARNING: line over 80 characters", I will change it back
in next version.
> if (cpu >= nr_cpu_ids) {
>- WARN_ON(1);
>- goto unlock;
>+ 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);
>+ }
Cool, I will fold this next branch in my patch, your help is a great appreciated. ;-)
Regards,
Wanpeng Li
> }
> later_rq = cpu_rq(cpu);
> double_lock_balance(rq, later_rq);
>--
>2.3.0
>
>On 02/03/2015 23:35, 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@...ux.intel.com>
>> ---
>> 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 | 40 ++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 40 insertions(+)
>>
>> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
>> index 08766a3..d5b1b16 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 +538,45 @@ 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) {
>> + WARN_ON(1);
>> + 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);
>> +
>> + if (!fallback)
>> + resched_curr(later_rq);
>> +
>> + double_unlock_balance(rq, later_rq);
>> +
>> + goto unlock;
>> + }
>> +
>> + /*
>> * If the throttle happened during sched-out; like:
>> *
>> * schedule()
>>
--
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