From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754268AbbDID3g (ORCPT ); Wed, 8 Apr 2015 23:29:36 -0400 Received: from m15-112.126.com ([220.181.15.112]:39775 "EHLO m15-112.126.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752889AbbDID3e (ORCPT ); Wed, 8 Apr 2015 23:29:34 -0400 From: Xunlei Pang To: linux-kernel@vger.kernel.org Cc: Peter Zijlstra , Steven Rostedt , Juri Lelli , Dan Streetman , Xunlei Pang Subject: [PATCH v5 3/3] sched/rt: Check to push the task when changing its affinity Date: Thu, 9 Apr 2015 11:27:18 +0800 Message-Id: <1428550038-13619-3-git-send-email-xlpang@126.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1428550038-13619-1-git-send-email-xlpang@126.com> References: <1428550038-13619-1-git-send-email-xlpang@126.com> X-CM-TRANSID: DMmowEDJvlOa8SVVTV0aAQ--.926S4 X-Coremail-Antispam: 1Uf129KBjvJXoWxXFy3Jr48KFy5ur4fAF1UJrb_yoWrCF13pa 1vk390gr4DJa1SgF1fZw4DZr45K3sYv34rJrnxtw1FkFs8tr4Fv3W5tF1ayF95ur1YgF4a qr4DtrsrKF1DZaDanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07b59a9UUUUU= X-Originating-IP: [210.21.223.3] X-CM-SenderInfo: p0ost0bj6rjloofrz/1tbimgLWv1GfV0Y-GgAAsL Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Xunlei Pang We may suffer from extra rt overload rq due to the affinity, so when the affinity of any runnable rt task is changed, we should check to trigger balancing, otherwise it will cause some unnecessary delayed real-time response. Unfortunately, current RT global scheduler doesn't trigger anything. For example: a 2-cpu system with two runnable FIFO tasks(same rt_priority) bound on CPU0, let's name them rt1(running) and rt2(runnable) respectively; CPU1 has no RTs. Then, someone sets the affinity of rt2 to 0x3(i.e. CPU0 and CPU1), but after this, rt2 still can't be scheduled until rt1 enters schedule(), this definitely causes some/big response latency for rt2. So, when doing set_cpus_allowed_rt(), if detecting such cases, check to trigger a push behaviour. Signed-off-by: Xunlei Pang --- kernel/sched/rt.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 71 insertions(+), 10 deletions(-) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 402162a..9704ed3 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1445,10 +1445,9 @@ static struct sched_rt_entity *pick_next_rt_entity(struct rq *rq, return next; } -static struct task_struct *_pick_next_task_rt(struct rq *rq) +static struct task_struct *peek_next_task_rt(struct rq *rq) { struct sched_rt_entity *rt_se; - struct task_struct *p; struct rt_rq *rt_rq = &rq->rt; do { @@ -1457,7 +1456,14 @@ static struct task_struct *_pick_next_task_rt(struct rq *rq) rt_rq = group_rt_rq(rt_se); } while (rt_rq); - p = rt_task_of(rt_se); + return rt_task_of(rt_se); +} + +static inline struct task_struct *_pick_next_task_rt(struct rq *rq) +{ + struct task_struct *p; + + p = peek_next_task_rt(rq); p->se.exec_start = rq_clock_task(rq); return p; @@ -2077,28 +2083,77 @@ static void set_cpus_allowed_rt(struct task_struct *p, const struct cpumask *new_mask) { struct rq *rq; - int weight; + int old_weight, new_weight; + int preempt_push = 0, direct_push = 0; BUG_ON(!rt_task(p)); if (!task_on_rq_queued(p)) return; - weight = cpumask_weight(new_mask); + old_weight = p->nr_cpus_allowed; + new_weight = cpumask_weight(new_mask); + rq = task_rq(p); + + if (new_weight > 1 && + rt_task(rq->curr) && + rq->rt.rt_nr_total > 1 && + !test_tsk_need_resched(rq->curr)) { + /* + * We own p->pi_lock and rq->lock. rq->lock might + * get released when doing direct pushing, however + * p->pi_lock is always held, so it's safe to assign + * new_mask and new_weight to p below. + */ + if (!task_running(rq, p)) { + cpumask_copy(&p->cpus_allowed, new_mask); + p->nr_cpus_allowed = new_weight; + direct_push = 1; + } else if (cpumask_test_cpu(task_cpu(p), new_mask)) { + struct task_struct *next; + + cpumask_copy(&p->cpus_allowed, new_mask); + p->nr_cpus_allowed = new_weight; + if (!cpupri_find(&rq->rd->cpupri, p, NULL)) + goto update; + + /* + * At this point, current task gets migratable most + * likely due to the change of its affinity, let's + * figure out if we can migrate it. + * + * Can we find any task with the same priority as + * current? To accomplish this, firstly we requeue + * current to the tail and peek next, then restore + * current to the head. + */ + requeue_task_rt(rq, p, 0); + next = peek_next_task_rt(rq); + requeue_task_rt(rq, p, 1); + if (next != p && next->prio == p->prio) { + /* + * Target found, so let's reschedule to try + * and push current away. + */ + requeue_task_rt(rq, next, 1); + preempt_push = 1; + } + } + } + +update: /* * Only update if the process changes its state from whether it * can migrate or not. */ - if ((p->nr_cpus_allowed > 1) == (weight > 1)) - return; - - rq = task_rq(p); + if ((old_weight > 1) == (new_weight > 1)) + goto out; /* * The process used to be able to migrate OR it can now migrate */ - if (weight <= 1) { + if (new_weight <= 1) { if (!task_current(rq, p)) dequeue_pushable_task(rq, p); BUG_ON(!rq->rt.rt_nr_migratory); @@ -2110,6 +2165,12 @@ static void set_cpus_allowed_rt(struct task_struct *p, } update_rt_migration(&rq->rt); + +out: + if (direct_push) + push_rt_tasks(rq); + else if (preempt_push) + resched_curr(rq); } /* Assumes rq->lock is held */ -- 1.9.1