sched debug: check spread

debug feature: check how well we schedule within a reasonable
vruntime 'spread' range. (note that CPU overload can increase
the spread, so this is not a hard condition, but normal loads
should be within the spread.)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

1 files changed, 17 insertions, 0 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 87acc5cedd2d..8ea4c9b3e411 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -447,6 +447,19 @@ static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
 #endif
 }
 
+static void check_spread(struct cfs_rq *cfs_rq, struct sched_entity *se)
+{
+#ifdef CONFIG_SCHED_DEBUG
+        s64 d = se->vruntime - cfs_rq->min_vruntime;
+
+        if (d < 0)
+                d = -d;
+
+        if (d > 3*sysctl_sched_latency)
+                schedstat_inc(cfs_rq, nr_spread_over);
+#endif
+}
+
 static void
 place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
 {
@@ -494,6 +507,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int wakeup)
         }
 
         update_stats_enqueue(cfs_rq, se);
+        check_spread(cfs_rq, se);
         if (se != cfs_rq->curr)
                 __enqueue_entity(cfs_rq, se);
         account_entity_enqueue(cfs_rq, se);
@@ -587,6 +601,7 @@ static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev)
 
         update_stats_curr_end(cfs_rq, prev);
 
+        check_spread(cfs_rq, prev);
         if (prev->on_rq) {
                 update_stats_wait_start(cfs_rq, prev);
                 /* Put 'current' back into the tree. */
@@ -996,6 +1011,8 @@ static void task_new_fair(struct rq *rq, struct task_struct *p)
         }
 
         update_stats_enqueue(cfs_rq, se);
+        check_spread(cfs_rq, se);
+        check_spread(cfs_rq, curr);
         __enqueue_entity(cfs_rq, se);
         account_entity_enqueue(cfs_rq, se);
         resched_task(rq->curr);