From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934570AbcI0RNn (ORCPT ); Tue, 27 Sep 2016 13:13:43 -0400 Received: from mail-pf0-f174.google.com ([209.85.192.174]:36682 "EHLO mail-pf0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750882AbcI0RNd (ORCPT ); Tue, 27 Sep 2016 13:13:33 -0400 From: bsegall@google.com To: Jeehong Kim Cc: mingo@redhat.com, linux-kernel@vger.kernel.org, ezjjilong@gmail.com, Peter Zijlstra 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. References: <57E38F55.9020601@samsung.com> <57E9EA5B.40904@samsung.com> Date: Tue, 27 Sep 2016 10:13:30 -0700 In-Reply-To: <57E9EA5B.40904@samsung.com> (Jeehong Kim's message of "Tue, 27 Sep 2016 12:41:15 +0900") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id u8RHDwgi010067 Jeehong Kim writes: > On 2016년 09월 23일 01:53, bsegall@google.com wrote: >> Jeehong Kim writes: >> >>>> Peter Zijlstra 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 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. Reviewed-By: Ben Segall (My understanding of signed-off-by is that I don't do that in this case)