From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752135AbaFXT0s (ORCPT ); Tue, 24 Jun 2014 15:26:48 -0400 Received: from forward4l.mail.yandex.net ([84.201.143.137]:58183 "EHLO forward4l.mail.yandex.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750853AbaFXT0r (ORCPT ); Tue, 24 Jun 2014 15:26:47 -0400 X-Yandex-Uniq: 449aa291-3a17-49c2-a1b6-7622f22e8d0e Authentication-Results: smtp11.mail.yandex.net; dkim=pass header.i=@yandex.ru Message-ID: <53A9D0F1.5080305@yandex.ru> Date: Tue, 24 Jun 2014 23:26:41 +0400 From: Kirill Tkhai Reply-To: tkhai@yandex.ru User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Icedove/24.5.0 MIME-Version: 1.0 To: bsegall@google.com CC: Kirill Tkhai , linux-kernel@vger.kernel.org, Peter Zijlstra , Ingo Molnar , Srikar Dronamraju , Mike Galbraith , khorenko@parallels.com, Paul Turner Subject: Re: [PATCH v2 1/3] sched/fair: Disable runtime_enabled on dying rq References: <20140624074148.8738.57690.stgit@tkhai> <1403596432.3462.26.camel@tkhai> <53A9CB23.1080708@yandex.ru> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 24.06.2014 23:13, bsegall@google.com wrote: > Kirill Tkhai writes: > >> On 24.06.2014 21:03, bsegall@google.com wrote: >>> Kirill Tkhai writes: >>> >>>> We kill rq->rd on the CPU_DOWN_PREPARE stage: >>>> >>>> cpuset_cpu_inactive -> cpuset_update_active_cpus -> partition_sched_domains -> >>>> -> cpu_attach_domain -> rq_attach_root -> set_rq_offline >>>> >>>> This unthrottles all throttled cfs_rqs. >>>> >>>> But the cpu is still able to call schedule() till >>>> >>>> take_cpu_down->__cpu_disable() >>>> >>>> is called from stop_machine. >>>> >>>> This case the tasks from just unthrottled cfs_rqs are pickable >>>> in a standard scheduler way, and they are picked by dying cpu. >>>> The cfs_rqs becomes throttled again, and migrate_tasks() >>>> in migration_call skips their tasks (one more unthrottle >>>> in migrate_tasks()->CPU_DYING does not happen, because rq->rd >>>> is already NULL). >>>> >>>> Patch sets runtime_enabled to zero. This guarantees, the runtime >>>> is not accounted, and the cfs_rqs won't exceed given >>>> cfs_rq->runtime_remaining = 1, and tasks will be pickable >>>> in migrate_tasks(). runtime_enabled is recalculated again >>>> when rq becomes online again. >>>> >>>> Ben Segall also noticed, we always enable runtime in >>>> tg_set_cfs_bandwidth(). Actually, we should do that for online >>>> cpus only. To fix that, we check if a cpu is online when >>>> its rq is locked. This guarantees we do not have races with >>>> set_rq_offline(), which also requires rq->lock. >>>> >>>> v2: Fix race with tg_set_cfs_bandwidth(). >>>> Move cfs_rq->runtime_enabled=0 above unthrottle_cfs_rq(). >>>> >>>> Signed-off-by: Kirill Tkhai >>>> CC: Konstantin Khorenko >>>> CC: Ben Segall >>>> CC: Paul Turner >>>> CC: Srikar Dronamraju >>>> CC: Mike Galbraith >>>> CC: Peter Zijlstra >>>> CC: Ingo Molnar >>>> --- >>>> kernel/sched/core.c | 15 +++++++++++---- >>>> kernel/sched/fair.c | 22 ++++++++++++++++++++++ >>>> 2 files changed, 33 insertions(+), 4 deletions(-) >>>> >>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >>>> index 7f3063c..707a3c5 100644 >>>> --- a/kernel/sched/core.c >>>> +++ b/kernel/sched/core.c >>>> @@ -7842,11 +7842,18 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota) >>>> struct rq *rq = cfs_rq->rq; >>>> >>>> raw_spin_lock_irq(&rq->lock); >>>> - cfs_rq->runtime_enabled = runtime_enabled; >>>> - cfs_rq->runtime_remaining = 0; >>>> + /* >>>> + * Do not enable runtime on offline runqueues. We specially >>>> + * make it disabled in unthrottle_offline_cfs_rqs(). >>>> + */ >>>> + if (cpu_online(i)) { >>>> + cfs_rq->runtime_enabled = runtime_enabled; >>>> + cfs_rq->runtime_remaining = 0; >>>> + >>>> + if (cfs_rq->throttled) >>>> + unthrottle_cfs_rq(cfs_rq); >>>> + } >>> >>> We can just do for_each_online_cpu, yes? Also we probably need >>> get_online_cpus/put_online_cpus, and/or want cpu_active_mask instead >>> right? >>> >> >> Yes, we can use for_each_online_cpu/for_each_active_cpu with >> get_online_cpus() taken. But it adds one more lock dependence. >> This looks worse for me. > > I mean, you need get_online_cpus anyway - cpu_online is just a test > against the same mask that for_each_online_cpu uses, and without taking > the lock you can still race with offlining and reset runtime_enabled. > Oh, I see. Thanks.