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-rw-r--r--kernel/sched_fair.c63
1 files changed, 57 insertions, 6 deletions
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 892616bf2c77..c9fbe8e73a45 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -43,6 +43,14 @@ unsigned int sysctl_sched_latency __read_mostly = 20000000ULL;
unsigned int sysctl_sched_min_granularity __read_mostly = 2000000ULL;
/*
+ * sys_sched_yield() compat mode
+ *
+ * This option switches the agressive yield implementation of the
+ * old scheduler back on.
+ */
+unsigned int __read_mostly sysctl_sched_compat_yield;
+
+/*
* SCHED_BATCH wake-up granularity.
* (default: 25 msec, units: nanoseconds)
*
@@ -897,19 +905,62 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int sleep)
}
/*
- * sched_yield() support is very simple - we dequeue and enqueue
+ * sched_yield() support is very simple - we dequeue and enqueue.
+ *
+ * If compat_yield is turned on then we requeue to the end of the tree.
*/
static void yield_task_fair(struct rq *rq, struct task_struct *p)
{
struct cfs_rq *cfs_rq = task_cfs_rq(p);
+ struct rb_node **link = &cfs_rq->tasks_timeline.rb_node;
+ struct sched_entity *rightmost, *se = &p->se;
+ struct rb_node *parent;
- __update_rq_clock(rq);
/*
- * Dequeue and enqueue the task to update its
- * position within the tree:
+ * Are we the only task in the tree?
+ */
+ if (unlikely(cfs_rq->nr_running == 1))
+ return;
+
+ if (likely(!sysctl_sched_compat_yield)) {
+ __update_rq_clock(rq);
+ /*
+ * Dequeue and enqueue the task to update its
+ * position within the tree:
+ */
+ dequeue_entity(cfs_rq, &p->se, 0);
+ enqueue_entity(cfs_rq, &p->se, 0);
+
+ return;
+ }
+ /*
+ * Find the rightmost entry in the rbtree:
*/
- dequeue_entity(cfs_rq, &p->se, 0);
- enqueue_entity(cfs_rq, &p->se, 0);
+ do {
+ parent = *link;
+ link = &parent->rb_right;
+ } while (*link);
+
+ rightmost = rb_entry(parent, struct sched_entity, run_node);
+ /*
+ * Already in the rightmost position?
+ */
+ if (unlikely(rightmost == se))
+ return;
+
+ /*
+ * Minimally necessary key value to be last in the tree:
+ */
+ se->fair_key = rightmost->fair_key + 1;
+
+ if (cfs_rq->rb_leftmost == &se->run_node)
+ cfs_rq->rb_leftmost = rb_next(&se->run_node);
+ /*
+ * Relink the task to the rightmost position:
+ */
+ rb_erase(&se->run_node, &cfs_rq->tasks_timeline);
+ rb_link_node(&se->run_node, parent, link);
+ rb_insert_color(&se->run_node, &cfs_rq->tasks_timeline);
}
/*