[tip: sched/core] sched/fair: Remove sched_feat(START_DEBIT)

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     e0c2ff903c320d3fd3c2c604dc401b3b7c0a1d13
Gitweb:        https://git.kernel.org/tip/e0c2ff903c320d3fd3c2c604dc401b3b7c0a1d13
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Wed, 31 May 2023 13:58:41 +02:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 19 Jul 2023 09:43:58 +02:00

sched/fair: Remove sched_feat(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@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230531124603.722361178@xxxxxxxxxxxxx
---
 kernel/sched/fair.c     | 21 +--------------------
 kernel/sched/features.h |  6 ------
 2 files changed, 1 insertion(+), 26 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bb54606..fc43482 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -906,16 +906,6 @@ static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
 	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_sleeper(struct sched_entity *se)
 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) {
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index ee7f23c..fa828b3 100644
--- 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.