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Message-ID: <20071017185032.11272.1916.stgit@novell1.haskins.net>
Date: Wed, 17 Oct 2007 14:50:32 -0400
From: Gregory Haskins <ghaskins@...ell.com>
To: Steven Rostedt <rostedt@...dmis.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: RT <linux-rt-users@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
LKML <linux-kernel@...r.kernel.org>,
Gregory Haskins <ghaskins@...ell.com>
Subject: [PATCH 1/9] RT: push-rt
From: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
kernel/sched.c | 141 ++++++++++++++++++++++++++++++++++++++++++++++++++---
kernel/sched_rt.c | 44 +++++++++++++++++
2 files changed, 178 insertions(+), 7 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index 3e75c62..0dabf89 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -304,6 +304,7 @@ struct rq {
#ifdef CONFIG_PREEMPT_RT
unsigned long rt_nr_running;
unsigned long rt_nr_uninterruptible;
+ int curr_prio;
#endif
unsigned long switch_timestamp;
@@ -1484,6 +1485,123 @@ next_in_queue:
static int double_lock_balance(struct rq *this_rq, struct rq *busiest);
+/* Only try this algorithm three times */
+#define RT_PUSH_MAX_TRIES 3
+
+/* Will lock the rq it finds */
+static struct rq *find_lock_lowest_rq(cpumask_t *cpu_mask,
+ struct task_struct *task,
+ struct rq *this_rq)
+{
+ struct rq *lowest_rq = NULL;
+ int dst_cpu = -1;
+ int cpu;
+ int tries;
+
+ for (tries = 0; tries < RT_PUSH_MAX_TRIES; tries++) {
+ /*
+ * Scan each rq for the lowest prio.
+ */
+ for_each_cpu_mask(cpu, *cpu_mask) {
+ struct rq *rq = &per_cpu(runqueues, cpu);
+
+ if (cpu == smp_processor_id())
+ continue;
+
+ /* We look for lowest RT prio or non-rt CPU */
+ if (rq->curr_prio >= MAX_RT_PRIO) {
+ lowest_rq = rq;
+ dst_cpu = cpu;
+ break;
+ }
+
+ /* no locking for now */
+ if (rq->curr_prio > task->prio &&
+ (!lowest_rq || rq->curr_prio < lowest_rq->curr_prio)) {
+ lowest_rq = rq;
+ dst_cpu = cpu;
+ }
+ }
+
+ if (!lowest_rq)
+ break;
+
+ /* if the prio of this runqueue changed, try again */
+ if (double_lock_balance(this_rq, lowest_rq)) {
+ /*
+ * We had to unlock the run queue. In
+ * the mean time, task could have
+ * migrated already or had its affinity changed.
+ */
+ if (unlikely(task_rq(task) != this_rq ||
+ !cpu_isset(dst_cpu, task->cpus_allowed))) {
+ spin_unlock(&lowest_rq->lock);
+ lowest_rq = NULL;
+ break;
+ }
+
+ }
+
+ /* If this rq is still suitable use it. */
+ if (lowest_rq->curr_prio > task->prio)
+ break;
+
+ /* try again */
+ spin_unlock(&lowest_rq->lock);
+ lowest_rq = NULL;
+ }
+
+ return lowest_rq;
+}
+
+/*
+ * If the current CPU has more than one RT task, see if the non
+ * running task can migrate over to a CPU that is running a task
+ * of lesser priority.
+ */
+static int push_rt_task(struct rq *this_rq)
+{
+ struct task_struct *next_task;
+ struct rq *lowest_rq;
+ int dst_cpu;
+ int ret = 0;
+ cpumask_t cpu_mask;
+
+ assert_spin_locked(&this_rq->lock);
+
+ next_task = rt_next_highest_task(this_rq);
+ if (!next_task)
+ return 0;
+
+ cpus_and(cpu_mask, cpu_online_map, next_task->cpus_allowed);
+
+ /* We might release this_rq lock */
+ get_task_struct(next_task);
+
+ /* find_lock_lowest_rq locks the rq if found */
+ lowest_rq = find_lock_lowest_rq(&cpu_mask, next_task, this_rq);
+ if (!lowest_rq)
+ goto out;
+
+ dst_cpu = lowest_rq->cpu;
+
+ assert_spin_locked(&lowest_rq->lock);
+
+ deactivate_task(this_rq, next_task, 0);
+ set_task_cpu(next_task, dst_cpu);
+ activate_task(lowest_rq, next_task, 0);
+
+ resched_task(lowest_rq->curr);
+
+ spin_unlock(&lowest_rq->lock);
+
+ ret = 1;
+out:
+ put_task_struct(next_task);
+
+ return ret;
+}
+
/*
* Pull RT tasks from other CPUs in the RT-overload
* case. Interrupts are disabled, local rq is locked.
@@ -2202,19 +2320,28 @@ static inline void finish_task_switch(struct rq *rq, struct task_struct *prev)
* be dropped twice.
* Manfred Spraul <manfred@...orfullife.com>
*/
+ prev_state = prev->state;
+ _finish_arch_switch(prev);
+#if defined(CONFIG_PREEMPT_RT) && defined(CONFIG_SMP)
+ rq->curr_prio = current->prio;
+#endif
+ finish_lock_switch(rq, prev);
#if defined(CONFIG_PREEMPT_RT) && defined(CONFIG_SMP)
/*
* If we pushed an RT task off the runqueue,
- * then kick other CPUs, they might run it:
+ * then kick other CPUs, they might run it.
+ * Note we may release the rq lock, and since
+ * the lock was owned by prev, we need to release it
+ * first via finish_lock_switch and then reaquire it.
*/
- if (unlikely(rt_task(current) && rq->rt_nr_running > 1)) {
- schedstat_inc(rq, rto_schedule);
- smp_send_reschedule_allbutself_cpumask(current->cpus_allowed);
+ if (unlikely(rt_task(current))) {
+ spin_lock(&rq->lock);
+ /* push_rt_task will return true if it moved an RT */
+ while (push_rt_task(rq))
+ ;
+ spin_unlock(&rq->lock);
}
#endif
- prev_state = prev->state;
- _finish_arch_switch(prev);
- finish_lock_switch(rq, prev);
fire_sched_in_preempt_notifiers(current);
trace_stop_sched_switched(current);
/*
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 369827b..8d59e62 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -96,6 +96,50 @@ static struct task_struct *pick_next_task_rt(struct rq *rq)
return next;
}
+#ifdef CONFIG_PREEMPT_RT
+static struct task_struct *rt_next_highest_task(struct rq *rq)
+{
+ struct rt_prio_array *array = &rq->rt.active;
+ struct task_struct *next;
+ struct list_head *queue;
+ int idx;
+
+ if (likely (rq->rt_nr_running < 2))
+ return NULL;
+
+ idx = sched_find_first_bit(array->bitmap);
+ if (idx >= MAX_RT_PRIO) {
+ WARN_ON(1); /* rt_nr_running is bad */
+ return NULL;
+ }
+
+ queue = array->queue + idx;
+ next = list_entry(queue->next, struct task_struct, run_list);
+ if (unlikely(next != current))
+ return next;
+
+ if (queue->next->next != queue) {
+ /* same prio task */
+ next = list_entry(queue->next->next, struct task_struct, run_list);
+ goto out;
+ }
+
+ /* slower, but more flexible */
+ idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
+ if (idx >= MAX_RT_PRIO) {
+ WARN_ON(1); /* rt_nr_running was 2 and above! */
+ return NULL;
+ }
+
+ queue = array->queue + idx;
+ next = list_entry(queue->next, struct task_struct, run_list);
+
+ out:
+ return next;
+
+}
+#endif /* CONFIG_PREEMPT_RT */
+
static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
{
update_curr_rt(rq);
-
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