Messages in this thread | | | Subject | 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. | From | Jeehong Kim <> | Date | Tue, 27 Sep 2016 12:41:15 +0900 |
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On 2016년 09월 23일 01:53, bsegall@google.com wrote: > Jeehong Kim <jhez.kim@samsung.com> writes: > >>> 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 > Oh, no, this is fine by me. > > >
Ben,
If this is fine to you, could you sign off on this patch?
Regards, Jeehong Kim.
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