sched: documentation: place_entity() comments

Add a few comments to place_entity(). No code changed.

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

1 files changed, 9 insertions, 2 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 62b057603f07..8763bee6b661 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -473,19 +473,26 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
         } else if (sched_feat(APPROX_AVG) && cfs_rq->nr_running)
                 vruntime += sched_vslice(cfs_rq)/2;
 
+        /*
+         * The 'current' period is already promised to the current tasks,
+         * however the extra weight of the new task will slow them down a
+         * little, place the new task so that it fits in the slot that
+         * stays open at the end.
+         */
         if (initial && sched_feat(START_DEBIT))
                 vruntime += sched_vslice_add(cfs_rq, se);
 
         if (!initial) {
+                /* sleeps upto a single latency don't count. */
                 if (sched_feat(NEW_FAIR_SLEEPERS) && entity_is_task(se) &&
                                 task_of(se)->policy != SCHED_BATCH)
                         vruntime -= sysctl_sched_latency;
 
-                vruntime = max_t(s64, vruntime, se->vruntime);
+                /* ensure we never gain time by being placed backwards. */
+                vruntime = max_vruntime(se->vruntime, vruntime);
         }
 
         se->vruntime = vruntime;
-
 }
 
 static void