sched: RT-balance, add new methods to sched_class

Dmitry Adamushko found that the current implementation of the RT
balancing code left out changes to the sched_setscheduler and
rt_mutex_setprio.

This patch addresses this issue by adding methods to the schedule classes
to handle being switched out of (switched_from) and being switched into
(switched_to) a sched_class. Also a method for changing of priorities
is also added (prio_changed).

This patch also removes some duplicate logic between rt_mutex_setprio and
sched_setscheduler.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

4 files changed, 179 insertions, 22 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 2368a0d882e..5834c7fb79a 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1152,6 +1152,18 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
 #endif
 }
 
+static inline void check_class_changed(struct rq *rq, struct task_struct *p,
+                                       const struct sched_class *prev_class,
+                                       int oldprio, int running)
+{
+        if (prev_class != p->sched_class) {
+                if (prev_class->switched_from)
+                        prev_class->switched_from(rq, p, running);
+                p->sched_class->switched_to(rq, p, running);
+        } else
+                p->sched_class->prio_changed(rq, p, oldprio, running);
+}
+
 #ifdef CONFIG_SMP
 
 /*
@@ -4017,6 +4029,7 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
         unsigned long flags;
         int oldprio, on_rq, running;
         struct rq *rq;
+        const struct sched_class *prev_class = p->sched_class;
 
         BUG_ON(prio < 0 || prio > MAX_PRIO);
 
@@ -4042,18 +4055,10 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
         if (on_rq) {
                 if (running)
                         p->sched_class->set_curr_task(rq);
+
                 enqueue_task(rq, p, 0);
-                /*
-                 * Reschedule if we are currently running on this runqueue and
-                 * our priority decreased, or if we are not currently running on
-                 * this runqueue and our priority is higher than the current's
-                 */
-                if (running) {
-                        if (p->prio > oldprio)
-                                resched_task(rq->curr);
-                } else {
-                        check_preempt_curr(rq, p);
-                }
+
+                check_class_changed(rq, p, prev_class, oldprio, running);
         }
         task_rq_unlock(rq, &flags);
 }
@@ -4253,6 +4258,7 @@ int sched_setscheduler(struct task_struct *p, int policy,
 {
         int retval, oldprio, oldpolicy = -1, on_rq, running;
         unsigned long flags;
+        const struct sched_class *prev_class = p->sched_class;
         struct rq *rq;
 
         /* may grab non-irq protected spin_locks */
@@ -4346,18 +4352,10 @@ recheck:
         if (on_rq) {
                 if (running)
                         p->sched_class->set_curr_task(rq);
+
                 activate_task(rq, p, 0);
-                /*
-                 * Reschedule if we are currently running on this runqueue and
-                 * our priority decreased, or if we are not currently running on
-                 * this runqueue and our priority is higher than the current's
-                 */
-                if (running) {
-                        if (p->prio > oldprio)
-                                resched_task(rq->curr);
-                } else {
-                        check_preempt_curr(rq, p);
-                }
+
+                check_class_changed(rq, p, prev_class, oldprio, running);
         }
         __task_rq_unlock(rq);
         spin_unlock_irqrestore(&p->pi_lock, flags);
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 10aa6e1ae3d..dfa18d55561 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1280,6 +1280,42 @@ static void task_new_fair(struct rq *rq, struct task_struct *p)
         resched_task(rq->curr);
 }
 
+/*
+ * Priority of the task has changed. Check to see if we preempt
+ * the current task.
+ */
+static void prio_changed_fair(struct rq *rq, struct task_struct *p,
+                              int oldprio, int running)
+{
+        /*
+         * Reschedule if we are currently running on this runqueue and
+         * our priority decreased, or if we are not currently running on
+         * this runqueue and our priority is higher than the current's
+         */
+        if (running) {
+                if (p->prio > oldprio)
+                        resched_task(rq->curr);
+        } else
+                check_preempt_curr(rq, p);
+}
+
+/*
+ * We switched to the sched_fair class.
+ */
+static void switched_to_fair(struct rq *rq, struct task_struct *p,
+                             int running)
+{
+        /*
+         * We were most likely switched from sched_rt, so
+         * kick off the schedule if running, otherwise just see
+         * if we can still preempt the current task.
+         */
+        if (running)
+                resched_task(rq->curr);
+        else
+                check_preempt_curr(rq, p);
+}
+
 /* Account for a task changing its policy or group.
  *
  * This routine is mostly called to set cfs_rq->curr field when a task
@@ -1318,6 +1354,9 @@ static const struct sched_class fair_sched_class = {
         .set_curr_task          = set_curr_task_fair,
         .task_tick              = task_tick_fair,
         .task_new               = task_new_fair,
+
+        .prio_changed           = prio_changed_fair,
+        .switched_to            = switched_to_fair,
 };
 
 #ifdef CONFIG_SCHED_DEBUG
diff --git a/kernel/sched_idletask.c b/kernel/sched_idletask.c
index ca5374860ae..ef7a2661fa1 100644
--- a/kernel/sched_idletask.c
+++ b/kernel/sched_idletask.c
@@ -69,6 +69,33 @@ static void set_curr_task_idle(struct rq *rq)
 {
 }
 
+static void switched_to_idle(struct rq *rq, struct task_struct *p,
+                             int running)
+{
+        /* Can this actually happen?? */
+        if (running)
+                resched_task(rq->curr);
+        else
+                check_preempt_curr(rq, p);
+}
+
+static void prio_changed_idle(struct rq *rq, struct task_struct *p,
+                              int oldprio, int running)
+{
+        /* This can happen for hot plug CPUS */
+
+        /*
+         * Reschedule if we are currently running on this runqueue and
+         * our priority decreased, or if we are not currently running on
+         * this runqueue and our priority is higher than the current's
+         */
+        if (running) {
+                if (p->prio > oldprio)
+                        resched_task(rq->curr);
+        } else
+                check_preempt_curr(rq, p);
+}
+
 /*
  * Simple, special scheduling class for the per-CPU idle tasks:
  */
@@ -94,5 +121,9 @@ const struct sched_class idle_sched_class = {
 
         .set_curr_task          = set_curr_task_idle,
         .task_tick              = task_tick_idle,
+
+        .prio_changed           = prio_changed_idle,
+        .switched_to            = switched_to_idle,
+
         /* no .task_new for idle tasks */
 };
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index a5a45104603..57fa3d96847 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -779,7 +779,92 @@ static void leave_domain_rt(struct rq *rq)
         if (rq->rt.overloaded)
                 rt_clear_overload(rq);
 }
+
+/*
+ * When switch from the rt queue, we bring ourselves to a position
+ * that we might want to pull RT tasks from other runqueues.
+ */
+static void switched_from_rt(struct rq *rq, struct task_struct *p,
+                           int running)
+{
+        /*
+         * If there are other RT tasks then we will reschedule
+         * and the scheduling of the other RT tasks will handle
+         * the balancing. But if we are the last RT task
+         * we may need to handle the pulling of RT tasks
+         * now.
+         */
+        if (!rq->rt.rt_nr_running)
+                pull_rt_task(rq);
+}
+#endif /* CONFIG_SMP */
+
+/*
+ * When switching a task to RT, we may overload the runqueue
+ * with RT tasks. In this case we try to push them off to
+ * other runqueues.
+ */
+static void switched_to_rt(struct rq *rq, struct task_struct *p,
+                           int running)
+{
+        int check_resched = 1;
+
+        /*
+         * If we are already running, then there's nothing
+         * that needs to be done. But if we are not running
+         * we may need to preempt the current running task.
+         * If that current running task is also an RT task
+         * then see if we can move to another run queue.
+         */
+        if (!running) {
+#ifdef CONFIG_SMP
+                if (rq->rt.overloaded && push_rt_task(rq) &&
+                    /* Don't resched if we changed runqueues */
+                    rq != task_rq(p))
+                        check_resched = 0;
+#endif /* CONFIG_SMP */
+                if (check_resched && p->prio < rq->curr->prio)
+                        resched_task(rq->curr);
+        }
+}
+
+/*
+ * Priority of the task has changed. This may cause
+ * us to initiate a push or pull.
+ */
+static void prio_changed_rt(struct rq *rq, struct task_struct *p,
+                            int oldprio, int running)
+{
+        if (running) {
+#ifdef CONFIG_SMP
+                /*
+                 * If our priority decreases while running, we
+                 * may need to pull tasks to this runqueue.
+                 */
+                if (oldprio < p->prio)
+                        pull_rt_task(rq);
+                /*
+                 * If there's a higher priority task waiting to run
+                 * then reschedule.
+                 */
+                if (p->prio > rq->rt.highest_prio)
+                        resched_task(p);
+#else
+                /* For UP simply resched on drop of prio */
+                if (oldprio < p->prio)
+                        resched_task(p);
 #endif /* CONFIG_SMP */
+        } else {
+                /*
+                 * This task is not running, but if it is
+                 * greater than the current running task
+                 * then reschedule.
+                 */
+                if (p->prio < rq->curr->prio)
+                        resched_task(rq->curr);
+        }
+}
+
 
 static void task_tick_rt(struct rq *rq, struct task_struct *p)
 {
@@ -837,8 +922,12 @@ const struct sched_class rt_sched_class = {
         .pre_schedule           = pre_schedule_rt,
         .post_schedule          = post_schedule_rt,
         .task_wake_up           = task_wake_up_rt,
+        .switched_from          = switched_from_rt,
 #endif
 
         .set_curr_task          = set_curr_task_rt,
         .task_tick              = task_tick_rt,
+
+        .prio_changed           = prio_changed_rt,
+        .switched_to            = switched_to_rt,
 };