From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754875AbaFYHxn (ORCPT ); Wed, 25 Jun 2014 03:53:43 -0400 Received: from relay.parallels.com ([195.214.232.42]:59655 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752483AbaFYHxl (ORCPT ); Wed, 25 Jun 2014 03:53:41 -0400 Message-ID: <1403682814.3462.33.camel@tkhai> Subject: Re: [PATCH v2 1/3] sched/fair: Disable runtime_enabled on dying rq From: Kirill Tkhai To: Ben Segall CC: , Peter Zijlstra , Ingo Molnar , Srikar Dronamraju , Mike Galbraith , , Paul Turner , Date: Wed, 25 Jun 2014 11:53:34 +0400 In-Reply-To: <53A9D0F1.5080305@yandex.ru> References: <20140624074148.8738.57690.stgit@tkhai> <1403596432.3462.26.camel@tkhai> <53A9CB23.1080708@yandex.ru> <53A9D0F1.5080305@yandex.ru> Organization: Parallels Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.8.5-2+b3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Originating-IP: [10.30.26.172] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org В Вт, 24/06/2014 в 23:26 +0400, Kirill Tkhai пишет: > 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. But we can check for rq->online, don't we? How about this? sched/fair: Disable runtime_enabled on dying rq 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(). v3: Check for rq->online instead of cpu_active. Signed-off-by: Kirill Tkhai diff --git a/kernel/sched/core.c b/kernel/sched/core.c index ceea8d0..4c163c9 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7837,11 +7837,17 @@ 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 + * disable it in unthrottle_offline_cfs_rqs(). + */ + if (rq->online) { + cfs_rq->runtime_enabled = runtime_enabled; + cfs_rq->runtime_remaining = 0; - if (cfs_rq->throttled) - unthrottle_cfs_rq(cfs_rq); + if (cfs_rq->throttled) + unthrottle_cfs_rq(cfs_rq); + } raw_spin_unlock_irq(&rq->lock); } if (runtime_was_enabled && !runtime_enabled) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 1f9c457..5616d23 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3776,6 +3776,19 @@ static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) hrtimer_cancel(&cfs_b->slack_timer); } +static void __maybe_unused update_runtime_enabled(struct rq *rq) +{ + struct cfs_rq *cfs_rq; + + for_each_leaf_cfs_rq(rq, cfs_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); + } +} + static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq) { struct cfs_rq *cfs_rq; @@ -3789,6 +3802,12 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq) * there's some valid quota amount */ cfs_rq->runtime_remaining = 1; + /* + * Offline rq is schedulable till cpu is completely disabled + * in take_cpu_down(), so we prevent new cfs throttling here. + */ + cfs_rq->runtime_enabled = 0; + if (cfs_rq_throttled(cfs_rq)) unthrottle_cfs_rq(cfs_rq); } @@ -3832,6 +3851,7 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg) return NULL; } static inline void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {} +static inline void update_runtime_enabled(struct rq *rq) {} static inline void unthrottle_offline_cfs_rqs(struct rq *rq) {} #endif /* CONFIG_CFS_BANDWIDTH */ @@ -7325,6 +7345,8 @@ void trigger_load_balance(struct rq *rq) static void rq_online_fair(struct rq *rq) { update_sysctl(); + + update_runtime_enabled(rq); } static void rq_offline_fair(struct rq *rq)