Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1472482 > unrolled 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.

Back to article view | Back to linux.kernel

Contents

  [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 <jhez.kim@samsung.com> - 2016-08-30 15:20 +0200
    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. Peter Zijlstra <peterz@infradead.org> - 2016-09-01 13:10 +0200
      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. Jeehong Kim <jhez.kim@samsung.com> - 2016-09-01 14:00 +0200
      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. bsegall@google.com - 2016-09-01 23:20 +0200

#1472482 — [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.

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();
 }
--

[toc] | [next] | [standalone]

#1474281

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);
> +	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();
>  }

Looks ok, performance on hotplug doesn't really matter. Ben, you happy
with this?

[toc] | [prev] | [next] | [standalone]

#1474355

Hello,

First of all, thanks for review. And I am sorry that I forgot to CC Ben.

The reason why I sent last mail twice is that I forgot including the comments for changes from PATCH V1.

Thanks and BR.

On 2016년 09월 01일 20:01, Peter Zijlstra wrote:
> 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);
>> +	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();
>>  }
> Looks ok, performance on hotplug doesn't really matter. Ben, you happy
> with this?
>
>
>

[toc] | [prev] | [next] | [standalone]

#1474619 — 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.

Peter Zijlstra <peterz@infradead.org> 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);
>> +	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();
>>  }
>
> 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.

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web