From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934991AbcIVQxH (ORCPT ); Thu, 22 Sep 2016 12:53:07 -0400 Received: from mail-pf0-f181.google.com ([209.85.192.181]:33188 "EHLO mail-pf0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934145AbcIVQxG (ORCPT ); Thu, 22 Sep 2016 12:53:06 -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> Date: Thu, 22 Sep 2016 09:53:02 -0700 In-Reply-To: <57E38F55.9020601@samsung.com> (Jeehong Kim's message of "Thu, 22 Sep 2016 16:59:17 +0900") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.