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* [PATCH V2] sched/fair: Fix that tasks are not constrained by cfs_b->quota on hotplug core, when hotplug core is offline and then online.
@ 2016-08-30 13:12 Jeehong Kim
  2016-09-01 11:01 ` Peter Zijlstra
  0 siblings, 1 reply; 9+ messages in thread
From: Jeehong Kim @ 2016-08-30 13:12 UTC (permalink / raw)
  To: mingo; +Cc: peterz, linux-kernel, kernel-janitors, ezjjilong, Jeehong Kim

In case that CONFIG_HOTPLUG_CPU and CONFIG_CFS_BANDWIDTH is turned on
and tasks in bandwidth controlled task group run on hotplug core,
the tasks are not controlled by cfs_b->quota when hotplug core is offline
and then online. The remaining tasks in task group consume all of
cfs_b->quota on other cores.

The cause of this problem is described as below:

1. When hotplug core is offline while tasks in task group run
on hotplug core, unregister_fair_sched_group() deletes
leaf_cfs_rq_list of tg->cfs_rq[cpu] from &rq_of(cfs_rq)->leaf_cfs_rq_list.

2. Then, when hotplug core is online, update_runtime_enabled()
registers cfs_b->quota on cfs_rq->runtime_enabled of all leaf cfs_rq
on runqueue. However, because this is before enqueue_entity() adds
&cfs_rq->leaf_cfs_rq_list on &rq_of(cfs_rq)->leaf_cfs_rq_list,
cfs->quota is not register on cfs_rq->runtime_enabled.

To resolve this problem, this patch makes update_runtime_enabled()
registers cfs_b->quota by using walk_tg_tree_from().

Signed-off-by: Jeehong Kim <jhez.kim@samsung.com>
---
V2: update_runtime_enabled() walks the whole tg tree,
instead of register quota on every enqueue.

kernel/sched/fair.c | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6488815..63b376d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4373,17 +4373,27 @@ static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
 	hrtimer_cancel(&cfs_b->slack_timer);
 }

-static void __maybe_unused update_runtime_enabled(struct rq *rq)
+static int __maybe_unused __update_runtime_enabled(struct task_group *tg, void *data)
 {
-	struct cfs_rq *cfs_rq;
+	struct rq *rq = data;
+	struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
+	struct cfs_bandwidth *cfs_b = &cfs_rq->tg->cfs_bandwidth;

-	for_each_leaf_cfs_rq(rq, cfs_rq) {
-		struct cfs_bandwidth *cfs_b = &cfs_rq->tg->cfs_bandwidth;
+	raw_spin_lock(&cfs_b->lock);
+	cfs_rq->runtime_enabled = cfs_b->quota != RUNTIME_INF;
+	raw_spin_unlock(&cfs_b->lock);

-		raw_spin_lock(&cfs_b->lock);
-		cfs_rq->runtime_enabled = cfs_b->quota != RUNTIME_INF;
-		raw_spin_unlock(&cfs_b->lock);
-	}
+	return 0;
+}
+
+static void __maybe_unused update_runtime_enabled(struct rq *rq)
+{
+	struct cfs_rq *cfs_rq = &rq->cfs;
+
+	/* register cfs_b->quota on the whole tg tree */
+	rcu_read_lock();
+	walk_tg_tree_from(cfs_rq->tg, __update_runtime_enabled, tg_nop, (void *)rq);
+	rcu_read_unlock();
 }
--

^ permalink raw reply related	[flat|nested] 9+ messages in thread
* Re: [PATCH V2] sched/fair: Fix that tasks are not constrained by cfs_b->quota on hotplug core, when hotplug core is offline and then online.
@ 2016-09-22  7:59 Jeehong Kim
  2016-09-22 16:53 ` bsegall
  0 siblings, 1 reply; 9+ messages in thread
From: Jeehong Kim @ 2016-09-22  7:59 UTC (permalink / raw)
  To: Ben Segall; +Cc: mingo, linux-kernel, ezjjilong, Peter Zijlstra

>Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:
>
>> You forgot to Cc Ben, who gave you feedback on v1, which is rather poor
>> style. Also, I don't see how kernel-janitors is relevant to this patch.
>> This is very much not a janitorial thing.
>>
>> (also, why send it twice?)
>>
>> On Tue, Aug 30, 2016 at 10:12:40PM +0900, Jeehong Kim wrote:
>>> In case that CONFIG_HOTPLUG_CPU and CONFIG_CFS_BANDWIDTH is turned on
>>> and tasks in bandwidth controlled task group run on hotplug core,
>>> the tasks are not controlled by cfs_b->quota when hotplug core is offline
>>> and then online. The remaining tasks in task group consume all of
>>> cfs_b->quota on other cores.
>>>
>>> The cause of this problem is described as below:
>>>
>>> 1. When hotplug core is offline while tasks in task group run
>>> on hotplug core, unregister_fair_sched_group() deletes
>>> leaf_cfs_rq_list of tg->cfs_rq[cpu] from &rq_of(cfs_rq)->leaf_cfs_rq_list.
>>>
>>> 2. Then, when hotplug core is online, update_runtime_enabled()
>>Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:
>
>> You forgot to Cc Ben, who gave you feedback on v1, which is rather poor
>> style. Also, I don't see how kernel-janitors is relevant to this patch.
>> This is very much not a janitorial thing.
>>
>> (also, why send it twice?)
>>
>> On Tue, Aug 30, 2016 at 10:12:40PM +0900, Jeehong Kim wrote:
>>> In case that CONFIG_HOTPLUG_CPU and CONFIG_CFS_BANDWIDTH is turned on
>>> and tasks in bandwidth controlled task group run on hotplug core,
>>> the tasks are not controlled by cfs_b->quota when hotplug core is offline
>>> and then online. The remaining tasks in task group consume all of
>>> cfs_b->quota on other cores.
>>>
>>> The cause of this problem is described as below:
>>>
>>> 1. When hotplug core is offline while tasks in task group run
>>> on hotplug core, unregister_fair_sched_group() deletes
>>> leaf_cfs_rq_list of tg->cfs_rq[cpu] from &rq_of(cfs_rq)->leaf_cfs_rq_list.
>>>
>>> 2. Then, when hotplug core is online, update_runtime_enabled()
>>> registers cfs_b->quota on cfs_rq->runtime_enabled of all leaf cfs_rq
>>> on runqueue. However, because this is before enqueue_entity() adds
>>> &cfs_rq->leaf_cfs_rq_list on &rq_of(cfs_rq)->leaf_cfs_rq_list,
>>> cfs->quota is not register on cfs_rq->runtime_enabled.
>>>
>>> To resolve this problem, this patch makes update_runtime_enabled()
>>> registers cfs_b->quota by using walk_tg_tree_from().
>>
>>
>>> +static int __maybe_unused __update_runtime_enabled(struct task_group *tg, void *data)
>>>  {
>>> +    struct rq *rq = data;
>>> +    struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
>>> +    struct cfs_bandwidth *cfs_b = &cfs_rq->tg->cfs_bandwidth;
>>>
>>> +    raw_spin_lock(&cfs_b->lock);
>>> +    raw_spin_unlock(&cfs_b->lock);
>>>
>>> +    return 0;
>>> +}
>>> +
>>> +static void __maybe_unused update_runtime_enabled(struct rq *rq)
>>> +{
>>> +    struct cfs_rq *cfs_rq = &rq->cfs;
>>> +
>>> +    /* register cfs_b->quota on the whole tg tree */
>>> +    rcu_read_lock();
>>> +    walk_tg_tree_from(cfs_rq->tg, __update_runtime_enabled, tg_nop, (void *)rq);
>>> +    rcu_read_unlock();
>>>  }
>>
>> Looks ok, performance on hotplug doesn't really matter. Ben, you happy
>> with this?
>
> I'm not 100% sure about the exact timings and mechanics of hotplug, but
> cfs-bandwidth wise this is ok. We may still have runtime_remaining = 1,
> or we may have < 0 and yet be unthrottled, but either case is ok, even
> if hotplug allows tasks to have migrated here already (I'm not sure,
> looking at the code).
>
> Now that I check again you can just loop over the list of tgs rather
> than the hierarchical walk_tg_tree_from, but there's certainly no harm
> in it.

Ben,

Is there additional revision which I have to do?
If so, could you let me know about that?

Regards,
Jeehong Kim

^ permalink raw reply	[flat|nested] 9+ messages in thread
* [PATCH V2] sched/fair: Fix that tasks are not constrained by cfs_b->quota on hotplug core, when hotplug core is offline and then online.
@ 2016-08-30 13:09 Jeehong Kim
  0 siblings, 0 replies; 9+ messages in thread
From: Jeehong Kim @ 2016-08-30 13:09 UTC (permalink / raw)
  To: mingo; +Cc: peterz, linux-kernel, kernel-janitors, ezjjilong, Jeehong Kim

In case that CONFIG_HOTPLUG_CPU and CONFIG_CFS_BANDWIDTH is turned on
and tasks in bandwidth controlled task group run on hotplug core,
the tasks are not controlled by cfs_b->quota when hotplug core is offline
and then online. The remaining tasks in task group consume all of
cfs_b->quota on other cores.

The cause of this problem is described as below:

1. When hotplug core is offline while tasks in task group run
on hotplug core, unregister_fair_sched_group() deletes
leaf_cfs_rq_list of tg->cfs_rq[cpu] from &rq_of(cfs_rq)->leaf_cfs_rq_list.

2. Then, when hotplug core is online, update_runtime_enabled()
registers cfs_b->quota on cfs_rq->runtime_enabled of all leaf cfs_rq
on runqueue. However, because this is before enqueue_entity() adds
&cfs_rq->leaf_cfs_rq_list on &rq_of(cfs_rq)->leaf_cfs_rq_list,
cfs->quota is not register on cfs_rq->runtime_enabled.

To resolve this problem, this patch makes update_runtime_enabled()
registers cfs_b->quota by using walk_tg_tree_from().

Signed-off-by: Jeehong Kim <jhez.kim@samsung.com>
---
 kernel/sched/fair.c | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6488815..63b376d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4373,17 +4373,27 @@ static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
 	hrtimer_cancel(&cfs_b->slack_timer);
 }

-static void __maybe_unused update_runtime_enabled(struct rq *rq)
+static int __maybe_unused __update_runtime_enabled(struct task_group *tg, void *data)
 {
-	struct cfs_rq *cfs_rq;
+	struct rq *rq = data;
+	struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
+	struct cfs_bandwidth *cfs_b = &cfs_rq->tg->cfs_bandwidth;

-	for_each_leaf_cfs_rq(rq, cfs_rq) {
-		struct cfs_bandwidth *cfs_b = &cfs_rq->tg->cfs_bandwidth;
+	raw_spin_lock(&cfs_b->lock);
+	cfs_rq->runtime_enabled = cfs_b->quota != RUNTIME_INF;
+	raw_spin_unlock(&cfs_b->lock);

-		raw_spin_lock(&cfs_b->lock);
-		cfs_rq->runtime_enabled = cfs_b->quota != RUNTIME_INF;
-		raw_spin_unlock(&cfs_b->lock);
-	}
+	return 0;
+}
+
+static void __maybe_unused update_runtime_enabled(struct rq *rq)
+{
+	struct cfs_rq *cfs_rq = &rq->cfs;
+
+	/* register cfs_b->quota on the whole tg tree */
+	rcu_read_lock();
+	walk_tg_tree_from(cfs_rq->tg, __update_runtime_enabled, tg_nop, (void *)rq);
+	rcu_read_unlock();
 }
--

^ permalink raw reply related	[flat|nested] 9+ messages in thread
end of thread, other threads:[~2016-09-27 17:13 UTC | newest]

Thread overview: 9+ messages (download: mbox.gz follow: Atom feed
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2016-08-30 13:12 [PATCH V2] sched/fair: Fix that tasks are not constrained by cfs_b->quota on hotplug core, when hotplug core is offline and then online Jeehong Kim
2016-09-01 11:01 ` Peter Zijlstra
2016-09-01 11:52   ` Jeehong Kim
2016-09-01 17:23   ` bsegall
  -- strict thread matches above, loose matches on Subject: below --
2016-09-22  7:59 Jeehong Kim
2016-09-22 16:53 ` bsegall
2016-09-27  3:41   ` Jeehong Kim
2016-09-27 17:13     ` bsegall
2016-08-30 13:09 Jeehong Kim

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