From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934078AbbBDBOl (ORCPT ); Tue, 3 Feb 2015 20:14:41 -0500 Received: from m15-114.126.com ([220.181.15.114]:38656 "EHLO m15-114.126.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754617AbbBDBOV (ORCPT ); Tue, 3 Feb 2015 20:14:21 -0500 From: Xunlei Pang To: linux-kernel@vger.kernel.org Cc: Peter Zijlstra , Steven Rostedt , Juri Lelli , Xunlei Pang Subject: [PATCH RESEND 1/2] sched/rt: Check to push the task when changing its affinity Date: Wed, 4 Feb 2015 09:12:20 +0800 Message-Id: <1423012341-30265-1-git-send-email-xlpang@126.com> X-Mailer: git-send-email 1.9.1 X-CM-TRANSID: DsmowADn8VwectFU_IBWAA--.619S2 X-Coremail-Antispam: 1Uf129KBjvJXoWxXFy3Jr48KFy5tryrCF47CFg_yoWrAF4Dpa 1vk390gr4UJay2gF1fZw4DZr13G3s3Z34rGrnayw1Fkan8tr4Fv3W5tF1ayr1a9r1j9F4a qr4ktr47WF1DZa7anT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07jk8n5UUUUU= X-Originating-IP: [210.21.223.3] X-CM-SenderInfo: p0ost0bj6rjloofrz/1tbiWwaWv1PM7BOkNwAAsH 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 | 69 +++++++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 59 insertions(+), 10 deletions(-) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index f4d4b07..4dacb6e 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1428,7 +1428,7 @@ 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 *_pick_next_task_rt(struct rq *rq, int peek_only) { struct sched_rt_entity *rt_se; struct task_struct *p; @@ -1441,7 +1441,8 @@ static struct task_struct *_pick_next_task_rt(struct rq *rq) } while (rt_rq); p = rt_task_of(rt_se); - p->se.exec_start = rq_clock_task(rq); + if (!peek_only) + p->se.exec_start = rq_clock_task(rq); return p; } @@ -1476,7 +1477,7 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev) put_prev_task(rq, prev); - p = _pick_next_task_rt(rq); + p = _pick_next_task_rt(rq, 0); /* The running task is never eligible for pushing */ dequeue_pushable_task(rq, p); @@ -1886,28 +1887,69 @@ 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) && + !test_tsk_need_resched(rq->curr)) { + /* + * Set new mask information to prepare pushing. + * It's safe to do this here. + */ + cpumask_copy(&p->cpus_allowed, new_mask); + p->nr_cpus_allowed = new_weight; + + if (task_running(rq, p) && + cpumask_test_cpu(task_cpu(p), new_mask) && + cpupri_find(&rq->rd->cpupri, p, NULL)) { + /* + * 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. + * + * Is there any task with the same priority as that + * of current task? If found one, we should resched. + * NOTE: The target may be unpushable. + */ + if (p->prio == rq->rt.highest_prio.next) { + /* One target just in pushable_tasks list. */ + requeue_task_rt(rq, p, 0); + preempt_push = 1; + } else if (rq->rt.rt_nr_total > 1) { + struct task_struct *next; + + requeue_task_rt(rq, p, 0); + /* peek only */ + next = _pick_next_task_rt(rq, 1); + if (next != p && next->prio == p->prio) + preempt_push = 1; + } + } else if (!task_running(rq, p)) + direct_push = 1; + } /* * 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); @@ -1919,6 +1961,13 @@ static void set_cpus_allowed_rt(struct task_struct *p, } update_rt_migration(&rq->rt); + +out: + if (direct_push) + push_rt_tasks(rq); + + if (preempt_push) + resched_curr(rq); } /* Assumes rq->lock is held */ -- 1.9.1