From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755845AbcIAVOy (ORCPT ); Thu, 1 Sep 2016 17:14:54 -0400 Received: from mail-pa0-f45.google.com ([209.85.220.45]:35248 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753086AbcIAVOi (ORCPT ); Thu, 1 Sep 2016 17:14:38 -0400 From: bsegall@google.com To: Peter Zijlstra Cc: Jeehong Kim , mingo@redhat.com, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org, ezjjilong@gmail.com 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: <1472562760-20842-1-git-send-email-jhez.kim@samsung.com> <20160901110132.GG10138@twins.programming.kicks-ass.net> Date: Thu, 01 Sep 2016 10:23:22 -0700 In-Reply-To: <20160901110132.GG10138@twins.programming.kicks-ass.net> (Peter Zijlstra's message of "Thu, 1 Sep 2016 13:01:32 +0200") 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 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); >> + 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.