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Subject[PATCH 02/15] sched/fair: Remove START_DEBIT
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@infradead.org>
---
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
@@ -906,16 +906,6 @@ 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

@@ -4862,16 +4852,7 @@ static inline bool entity_is_long_sleepe
static void
place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
{
- u64 vruntime = cfs_rq->min_vruntime;
-
- /*
- * 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);
+ u64 vruntime = avg_vruntime(cfs_rq);

/* sleeps up to a single latency don't count. */
if (!initial) {
--- 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.

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