[PATCH 6/6] sched: place_entity() comments

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

[-- Attachment #1: sched-place-entity.patch --]
[-- Type: text/plain, Size: 1292 bytes --]

Add a few comments to place_entity().

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 kernel/sched_fair.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

Index: linux-2.6/kernel/sched_fair.c
===================================================================
--- linux-2.6.orig/kernel/sched_fair.c
+++ linux-2.6/kernel/sched_fair.c
@@ -582,19 +582,26 @@ place_entity(struct cfs_rq *cfs_rq, stru
 	} 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

--