From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966189AbeEJPGe (ORCPT ); Thu, 10 May 2018 11:06:34 -0400 Received: from foss.arm.com ([217.140.101.70]:57362 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966159AbeEJPGQ (ORCPT ); Thu, 10 May 2018 11:06:16 -0400 From: Patrick Bellasi To: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org Cc: Ingo Molnar , Peter Zijlstra , "Rafael J . Wysocki" , Viresh Kumar , Vincent Guittot , Dietmar Eggemann , Morten Rasmussen , Juri Lelli , Joel Fernandes , Steve Muckle Subject: [PATCH 3/3] sched/fair: schedutil: explicit update only when required Date: Thu, 10 May 2018 16:05:53 +0100 Message-Id: <20180510150553.28122-4-patrick.bellasi@arm.com> X-Mailer: git-send-email 2.15.1 In-Reply-To: <20180510150553.28122-1-patrick.bellasi@arm.com> References: <20180510150553.28122-1-patrick.bellasi@arm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Schedutil updates for FAIR tasks are triggered implicitly each time a cfs_rq's utilization is updated via cfs_rq_util_change(), currently called by update_cfs_rq_load_avg(), when the utilization of a cfs_rq has changed, and {attach,detach}_entity_load_avg(). This design is based on the idea that "we should callback schedutil frequently enough" to properly update the CPU frequency at every utilization change. However, such an integration strategy has also some downsides: - schedutil updates are triggered by RQ's load updates, which makes sense in general but it does not allow to know exactly which other RQ related information have been updated. Recently, for example, we had issues due to schedutil dependencies on cfs_rq->h_nr_running and estimated utilization updates. - cfs_rq_util_change() is mainly a wrapper function for an already existing "public API", cpufreq_update_util(), which is required just to ensure we actually update schedutil only when we are updating a root cfs_rq. Thus, especially when task groups are in use, most of the calls to this wrapper function are not required. - the usage of a wrapper function is not completely consistent across fair.c, since we could still need additional explicit calls to cpufreq_update_util(). For example this already happens to report the IOWAIT boot flag in the wakeup path. - it makes it hard to integrate new features since it could require to change other function prototypes just to pass in an additional flag, as it happened for example in commit: ea14b57e8a18 ("sched/cpufreq: Provide migration hint") All the above considered, let's make schedutil updates more explicit in fair.c by removing the cfs_rq_util_change() wrapper function in favour of the existing cpufreq_update_util() public API. This can be done by calling cpufreq_update_util() explicitly in the few call sites where it really makes sense and when all the (potentially) required cfs_rq's information have been updated. This patch mainly removes code and adds explicit schedutil updates only when we: - {enqueue,dequeue}_task_fair() a task to/from the root cfs_rq - (un)throttle_cfs_rq() a set of tasks up to the root cfs_rq - task_tick_fair() to update the utilization of the root cfs_rq All the other code paths, currently _indirectly_ covered by a call to update_load_avg(), are still covered. Indeed, some paths already imply enqueue/dequeue calls: - switch_{to,from}_fair() - sched_move_task() while others are followed by enqueue/dequeue calls: - cpu_cgroup_fork() and post_init_entity_util_avg(): are used at wakeup_new_task() time and thus already followed by an enqueue_task_fair() - migrate_task_rq_fair(): updates the removed utilization but not the actual cfs_rq utilization, which is updated by a following sched event This new proposal allows also to better aggregate schedutil related flags, which are required only at enqueue_task_fair() time. IOWAIT and MIGRATION flags are now requested only when a task is actually visible at the root cfs_rq level. Signed-off-by: Patrick Bellasi Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Rafael J. Wysocki Cc: Viresh Kumar Cc: Joel Fernandes Cc: Juri Lelli Cc: linux-kernel@vger.kernel.org Cc: linux-pm@vger.kernel.org --- NOTE: this patch changes the behavior of the IOWAIT flag: in case of a task waking up on a throttled RQ we do not assert the flag to schedutil anymore. However, this seems to make sense since the task will not be running anyway. --- kernel/sched/fair.c | 81 ++++++++++++++++++++++++----------------------------- 1 file changed, 36 insertions(+), 45 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 01dfc47541e6..87f092151a6e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -772,7 +772,7 @@ void post_init_entity_util_avg(struct sched_entity *se) * For !fair tasks do: * update_cfs_rq_load_avg(now, cfs_rq); - attach_entity_load_avg(cfs_rq, se, 0); + attach_entity_load_avg(cfs_rq, se); switched_from_fair(rq, p); * * such that the next switched_to_fair() has the @@ -3009,29 +3009,6 @@ static inline void update_cfs_group(struct sched_entity *se) } #endif /* CONFIG_FAIR_GROUP_SCHED */ -static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq, int flags) -{ - struct rq *rq = rq_of(cfs_rq); - - if (&rq->cfs == cfs_rq || (flags & SCHED_CPUFREQ_MIGRATION)) { - /* - * There are a few boundary cases this might miss but it should - * get called often enough that that should (hopefully) not be - * a real problem. - * - * It will not get called when we go idle, because the idle - * thread is a different class (!fair), nor will the utilization - * number include things like RT tasks. - * - * As is, the util number is not freq-invariant (we'd have to - * implement arch_scale_freq_capacity() for that). - * - * See cpu_util(). - */ - cpufreq_update_util(rq, flags); - } -} - #ifdef CONFIG_SMP /* * Approximate: @@ -3712,9 +3689,6 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) cfs_rq->load_last_update_time_copy = sa->last_update_time; #endif - if (decayed) - cfs_rq_util_change(cfs_rq, 0); - return decayed; } @@ -3726,7 +3700,7 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) * Must call update_cfs_rq_load_avg() before this, since we rely on * cfs_rq->avg.last_update_time being current. */ -static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) +static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) { u32 divider = LOAD_AVG_MAX - 1024 + cfs_rq->avg.period_contrib; @@ -3762,7 +3736,6 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s add_tg_cfs_propagate(cfs_rq, se->avg.load_sum); - cfs_rq_util_change(cfs_rq, flags); } /** @@ -3781,7 +3754,6 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s add_tg_cfs_propagate(cfs_rq, -se->avg.load_sum); - cfs_rq_util_change(cfs_rq, 0); } /* @@ -3818,7 +3790,7 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s * * IOW we're enqueueing a task on a new CPU. */ - attach_entity_load_avg(cfs_rq, se, SCHED_CPUFREQ_MIGRATION); + attach_entity_load_avg(cfs_rq, se); update_tg_load_avg(cfs_rq, 0); } else if (decayed && (flags & UPDATE_TG)) @@ -4028,13 +4000,12 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int not_used1) { - cfs_rq_util_change(cfs_rq, 0); } static inline void remove_entity_load_avg(struct sched_entity *se) {} static inline void -attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) {} +attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {} static inline void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {} @@ -4762,8 +4733,11 @@ static void throttle_cfs_rq(struct cfs_rq *cfs_rq) dequeue = 0; } - if (!se) + /* The tasks are no more visible from the root cfs_rq */ + if (!se) { sub_nr_running(rq, task_delta); + cpufreq_update_util(rq, 0); + } cfs_rq->throttled = 1; cfs_rq->throttled_clock = rq_clock(rq); @@ -4825,8 +4799,11 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq) break; } - if (!se) + /* The tasks are now visible from the root cfs_rq */ + if (!se) { add_nr_running(rq, task_delta); + cpufreq_update_util(rq, 0); + } /* Determine whether we need to wake up potentially idle CPU: */ if (rq->curr == rq->idle && rq->cfs.nr_running) @@ -5359,14 +5336,6 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) /* Estimated utilization must be updated before schedutil */ util_est_enqueue(&rq->cfs, p); - /* - * If in_iowait is set, the code below may not trigger any cpufreq - * utilization updates, so do it here explicitly with the IOWAIT flag - * passed. - */ - if (p->in_iowait) - cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT); - for_each_sched_entity(se) { if (se->on_rq) break; @@ -5397,9 +5366,27 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) update_cfs_group(se); } - if (!se) + /* The task is visible from the root cfs_rq */ + if (!se) { + unsigned int flags = 0; + add_nr_running(rq, 1); + if (p->in_iowait) + flags |= SCHED_CPUFREQ_IOWAIT; + + /* + * !last_update_time means we've passed through + * migrate_task_rq_fair() indicating we migrated. + * + * IOW we're enqueueing a task on a new CPU. + */ + if (!p->se.avg.last_update_time) + flags |= SCHED_CPUFREQ_MIGRATION; + + cpufreq_update_util(rq, flags); + } + hrtick_update(rq); } @@ -5456,10 +5443,12 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) update_cfs_group(se); } + /* The task is no more visible from the root cfs_rq */ if (!se) sub_nr_running(rq, 1); util_est_dequeue(&rq->cfs, p, task_sleep); + cpufreq_update_util(rq, 0); hrtick_update(rq); } @@ -9945,6 +9934,8 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued) if (static_branch_unlikely(&sched_numa_balancing)) task_tick_numa(rq, curr); + + cpufreq_update_util(rq, 0); } /* @@ -10082,7 +10073,7 @@ static void attach_entity_cfs_rq(struct sched_entity *se) /* Synchronize entity with its cfs_rq */ update_load_avg(cfs_rq, se, sched_feat(ATTACH_AGE_LOAD) ? 0 : SKIP_AGE_LOAD); - attach_entity_load_avg(cfs_rq, se, 0); + attach_entity_load_avg(cfs_rq, se); update_tg_load_avg(cfs_rq, false); propagate_entity_cfs_rq(se); } -- 2.15.1