[PATCH 07/10] sched/fair: Remove START_DEBIT

[Peter Zijlstra]

With the introduction of avg_vruntime() there is no need to use worse
approximations. Take the 0-lag point as starting point for inserting
new tasks.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/sched/fair.c     |   21 +--------------------
 kernel/sched/features.h |    6 ------
 2 files changed, 1 insertion(+), 26 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -882,16 +882,6 @@ static u64 sched_slice(struct cfs_rq *cf
 	return slice;
 }
 
-/*
- * We calculate the vruntime slice of a to-be-inserted task.
- *
- * vs = s/w
- */
-static u64 sched_vslice(struct cfs_rq *cfs_rq, struct sched_entity *se)
-{
-	return calc_delta_fair(sched_slice(cfs_rq, se), se);
-}
-
 #include "pelt.h"
 #ifdef CONFIG_SMP
 
@@ -4758,18 +4748,9 @@ static void check_spread(struct cfs_rq *
 static void
 place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
 {
-	u64 vruntime = cfs_rq->min_vruntime;
+	u64 vruntime = avg_vruntime(cfs_rq);
 	u64 sleep_time;
 
-	/*
-	 * 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(cfs_rq, se);
-
 	/* sleeps up to a single latency don't count. */
 	if (!initial) {
 		unsigned long thresh;
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -7,12 +7,6 @@
 SCHED_FEAT(GENTLE_FAIR_SLEEPERS, true)
 
 /*
- * Place new tasks ahead so that they do not starve already running
- * tasks
- */
-SCHED_FEAT(START_DEBIT, true)
-
-/*
  * Prefer to schedule the task we woke last (assuming it failed
  * wakeup-preemption), since its likely going to consume data we
  * touched, increases cache locality.