linux-kernel - [PATCH 1/2] sched/fair: Remove SCHED_FEAT(UTIL_EST

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Message-Id: <20231127143238.1216582-2-vincent.guittot@linaro.org>
Date:   Mon, 27 Nov 2023 15:32:37 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        corbet@....net, alexs@...nel.org, siyanteng@...ngson.cn,
        qyousef@...alina.io, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Cc:     lukasz.luba@....com, hongyan.xia2@....com,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH 1/2] sched/fair: Remove SCHED_FEAT(UTIL_EST_FASTUP, true)

sched_feat(UTIL_EST_FASTUP) has been added to easily disable the feature
in order to check for possibly related regressions. After 3 years, it has
never been used and no regression has been reported. Let remove it
and make fast increase a permanent behavior.

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---

I haven't updated the chinese documentation which also refers to
UTIL_EST_FASTUP. IIUC, this will be updated afterward by the 
Translations' maintainers.

 Documentation/scheduler/schedutil.rst | 7 +++----
 kernel/sched/fair.c                   | 8 +++-----
 kernel/sched/features.h               | 1 -
 3 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/Documentation/scheduler/schedutil.rst b/Documentation/scheduler/schedutil.rst
index 32c7d69fc86c..803fba8fc714 100644
--- a/Documentation/scheduler/schedutil.rst
+++ b/Documentation/scheduler/schedutil.rst
@@ -90,8 +90,8 @@ For more detail see:
  - Documentation/scheduler/sched-capacity.rst:"1. CPU Capacity + 2. Task utilization"
 
 
-UTIL_EST / UTIL_EST_FASTUP
-==========================
+UTIL_EST
+========
 
 Because periodic tasks have their averages decayed while they sleep, even
 though when running their expected utilization will be the same, they suffer a
@@ -99,8 +99,7 @@ though when running their expected utilization will be the same, they suffer a
 
 To alleviate this (a default enabled option) UTIL_EST drives an Infinite
 Impulse Response (IIR) EWMA with the 'running' value on dequeue -- when it is
-highest. A further default enabled option UTIL_EST_FASTUP modifies the IIR
-filter to instantly increase and only decay on decrease.
+highest. UTIL_EST filters to instantly increase and only decay on decrease.
 
 A further runqueue wide sum (of runnable tasks) is maintained of:
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 34fe6e9490c2..146329678cb8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4870,11 +4870,9 @@ static inline void util_est_update(struct cfs_rq *cfs_rq,
 	 * to smooth utilization decreases.
 	 */
 	ue.enqueued = task_util(p);
-	if (sched_feat(UTIL_EST_FASTUP)) {
-		if (ue.ewma < ue.enqueued) {
-			ue.ewma = ue.enqueued;
-			goto done;
-		}
+	if (ue.ewma < ue.enqueued) {
+		ue.ewma = ue.enqueued;
+		goto done;
 	}
 
 	/*
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index a3ddf84de430..143f55df890b 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -83,7 +83,6 @@ SCHED_FEAT(WA_BIAS, true)
  * UtilEstimation. Use estimated CPU utilization.
  */
 SCHED_FEAT(UTIL_EST, true)
-SCHED_FEAT(UTIL_EST_FASTUP, true)
 
 SCHED_FEAT(LATENCY_WARN, false)
 
-- 
2.34.1