From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933600AbcI0Dki (ORCPT ); Mon, 26 Sep 2016 23:40:38 -0400 Received: from mailout4.samsung.com ([203.254.224.34]:33325 "EHLO mailout4.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751340AbcI0Dkb (ORCPT ); Mon, 26 Sep 2016 23:40:31 -0400 MIME-version: 1.0 Content-type: text/plain; charset=UTF-8 X-AuditID: cbfee61a-f79786d000004c78-e4-57e9ea2dcf64 Content-transfer-encoding: 8BIT 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. To: bsegall@google.com References: <57E38F55.9020601@samsung.com> Cc: mingo@redhat.com, linux-kernel@vger.kernel.org, ezjjilong@gmail.com, Peter Zijlstra From: Jeehong Kim Message-id: <57E9EA5B.40904@samsung.com> Date: Tue, 27 Sep 2016 12:41:15 +0900 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 In-reply-to: X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFtrDIsWRmVeSWpSXmKPExsVy+t9jQV3dVy/DDY5skLKY/rKRxeLQv92M Ft1v+tgtTs4+z2hx9egkZovLu+awWVw6sIDJ4njvASYHDo+ds+6yeyzYVOqxeYWWx/t9V9k8 +rasYvT4vEkugC3KzSYjNTEltUghNS85PyUzL91WKTTETddCSSEvMTfVVilC1zckSEmhLDGn FMgzMkADDs4B7sFK+nYJbhnPe/+zFtxWrJhz/BVLA+Mx6S5GTg4JAROJexd3sUHYYhIX7q0H srk4hARmMUpMbuxhBknwCghK/Jh8j6WLkYODWUBe4silbJAws4C6xKR5i5gh6u8zSky9fIAR xBEWmM4ocfHYGhaQKhGgqTMfzICaupVR4tDs1awQkwokLu5TAqlhE9CQuNt8jwVimYZEy9OF TCA2i4CqxK093YwgtqhAhMTECQ2sIDangKPEwm1/mScwAp2JcN8shPtmIblvASPzKkaJ1ILk guKk9FzDvNRyveLE3OLSvHS95PzcTYzgmHsmtYPx4C73Q4wCHIxKPLw/Ol+GC7EmlhVX5h5i lOBgVhLhXfkUKMSbklhZlVqUH19UmpNafIjRFOjGicxSosn5wHSQVxJvaGJuYm5sYGFuaWli pCTO2zj7WbiQQHpiSWp2ampBahFMHxMHp1QD49Fl75fN3GOzQOJP4BRHfp+Iu66pygZrtrge 353hNfeCxRVT3cLXz3LzZqd8e/Nl97tYj/UrN2dH9KYeXbZaM/DEBh2BzRkNTSuLHjtWlU/l jvy70Unj+8USFjuVY1PjvjempgnuO/7IxYl7ikz8rmmx3A45N69ECUeEbC3Jm2n14OflQKmY K0osxRmJhlrMRcWJAAYZVpbPAgAA X-MTR: 20000000000000000@CPGS Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.