sched: track the next-highest priority on each runqueue

We will use this later in the series to reduce the amount of rq-lock
contention during a pull operation

Signed-off-by: Gregory Haskins <ghaskins@novell.com>

1 files changed, 61 insertions, 20 deletions

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 0a5277233452..ad36d7232236 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -108,7 +108,7 @@ static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
         if (rt_rq->rt_nr_running) {
                 if (rt_se && !on_rt_rq(rt_se))
                         enqueue_rt_entity(rt_se);
-                if (rt_rq->highest_prio < curr->prio)
+                if (rt_rq->highest_prio.curr < curr->prio)
                         resched_task(curr);
         }
 }
@@ -473,7 +473,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
         struct rt_rq *rt_rq = group_rt_rq(rt_se);
 
         if (rt_rq)
-                return rt_rq->highest_prio;
+                return rt_rq->highest_prio.curr;
 #endif
 
         return rt_task_of(rt_se)->prio;
@@ -547,6 +547,21 @@ static void update_curr_rt(struct rq *rq)
         }
 }
 
+#if defined CONFIG_SMP || defined CONFIG_RT_GROUP_SCHED
+
+static struct task_struct *pick_next_highest_task_rt(struct rq *rq, int cpu);
+
+static inline int next_prio(struct rq *rq)
+{
+        struct task_struct *next = pick_next_highest_task_rt(rq, rq->cpu);
+
+        if (next && rt_prio(next->prio))
+                return next->prio;
+        else
+                return MAX_RT_PRIO;
+}
+#endif
+
 static inline
 void inc_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
 {
@@ -558,14 +573,32 @@ void inc_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
         WARN_ON(!rt_prio(prio));
         rt_rq->rt_nr_running++;
 #if defined CONFIG_SMP || defined CONFIG_RT_GROUP_SCHED
-        if (prio < rt_rq->highest_prio) {
+        if (prio < rt_rq->highest_prio.curr) {
 
-                rt_rq->highest_prio = prio;
+                /*
+                 * If the new task is higher in priority than anything on the
+                 * run-queue, we have a new high that must be published to
+                 * the world.  We also know that the previous high becomes
+                 * our next-highest.
+                 */
+                rt_rq->highest_prio.next = rt_rq->highest_prio.curr;
+                rt_rq->highest_prio.curr = prio;
 #ifdef CONFIG_SMP
                 if (rq->online)
                         cpupri_set(&rq->rd->cpupri, rq->cpu, prio);
 #endif
-        }
+        } else if (prio == rt_rq->highest_prio.curr)
+                /*
+                 * If the next task is equal in priority to the highest on
+                 * the run-queue, then we implicitly know that the next highest
+                 * task cannot be any lower than current
+                 */
+                rt_rq->highest_prio.next = prio;
+        else if (prio < rt_rq->highest_prio.next)
+                /*
+                 * Otherwise, we need to recompute next-highest
+                 */
+                rt_rq->highest_prio.next = next_prio(rq);
 #endif
 #ifdef CONFIG_SMP
         if (rt_se->nr_cpus_allowed > 1)
@@ -589,7 +622,7 @@ void dec_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
 {
 #ifdef CONFIG_SMP
         struct rq *rq = rq_of_rt_rq(rt_rq);
-        int highest_prio = rt_rq->highest_prio;
+        int highest_prio = rt_rq->highest_prio.curr;
 #endif
 
         WARN_ON(!rt_prio(rt_se_prio(rt_se)));
@@ -597,24 +630,32 @@ void dec_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
         rt_rq->rt_nr_running--;
 #if defined CONFIG_SMP || defined CONFIG_RT_GROUP_SCHED
         if (rt_rq->rt_nr_running) {
-                struct rt_prio_array *array;
+                int prio = rt_se_prio(rt_se);
+
+                WARN_ON(prio < rt_rq->highest_prio.curr);
 
-                WARN_ON(rt_se_prio(rt_se) < rt_rq->highest_prio);
-                if (rt_se_prio(rt_se) == rt_rq->highest_prio) {
-                        /* recalculate */
-                        array = &rt_rq->active;
-                        rt_rq->highest_prio =
+                /*
+                 * This may have been our highest or next-highest priority
+                 * task and therefore we may have some recomputation to do
+                 */
+                if (prio == rt_rq->highest_prio.curr) {
+                        struct rt_prio_array *array = &rt_rq->active;
+
+                        rt_rq->highest_prio.curr =
                                 sched_find_first_bit(array->bitmap);
-                } /* otherwise leave rq->highest prio alone */
+                }
+
+                if (prio <= rt_rq->highest_prio.next)
+                        rt_rq->highest_prio.next = next_prio(rq);
         } else
-                rt_rq->highest_prio = MAX_RT_PRIO;
+                rt_rq->highest_prio.curr = MAX_RT_PRIO;
 #endif
 #ifdef CONFIG_SMP
         if (rt_se->nr_cpus_allowed > 1)
                 rq->rt.rt_nr_migratory--;
 
-        if (rq->online && rt_rq->highest_prio != highest_prio)
-                cpupri_set(&rq->rd->cpupri, rq->cpu, rt_rq->highest_prio);
+        if (rq->online && rt_rq->highest_prio.curr != highest_prio)
+                cpupri_set(&rq->rd->cpupri, rq->cpu, rt_rq->highest_prio.curr);
 
         update_rt_migration(rq);
 #endif /* CONFIG_SMP */
@@ -1064,7 +1105,7 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
                 }
 
                 /* If this rq is still suitable use it. */
-                if (lowest_rq->rt.highest_prio > task->prio)
+                if (lowest_rq->rt.highest_prio.curr > task->prio)
                         break;
 
                 /* try again */
@@ -1252,7 +1293,7 @@ static int pull_rt_task(struct rq *this_rq)
 static void pre_schedule_rt(struct rq *rq, struct task_struct *prev)
 {
         /* Try to pull RT tasks here if we lower this rq's prio */
-        if (unlikely(rt_task(prev)) && rq->rt.highest_prio > prev->prio)
+        if (unlikely(rt_task(prev)) && rq->rt.highest_prio.curr > prev->prio)
                 pull_rt_task(rq);
 }
 
@@ -1338,7 +1379,7 @@ static void rq_online_rt(struct rq *rq)
 
         __enable_runtime(rq);
 
-        cpupri_set(&rq->rd->cpupri, rq->cpu, rq->rt.highest_prio);
+        cpupri_set(&rq->rd->cpupri, rq->cpu, rq->rt.highest_prio.curr);
 }
 
 /* Assumes rq->lock is held */
@@ -1429,7 +1470,7 @@ static void prio_changed_rt(struct rq *rq, struct task_struct *p,
                  * can release the rq lock and p could migrate.
                  * Only reschedule if p is still on the same runqueue.
                  */
-                if (p->prio > rq->rt.highest_prio && rq->curr == p)
+                if (p->prio > rq->rt.highest_prio.curr && rq->curr == p)
                         resched_task(p);
 #else
                 /* For UP simply resched on drop of prio */