Re: [PATCH v2 1/2] sched/fair: Remove SCHED_FEAT(UTIL_EST_FASTUP, true)

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在 2023/12/2 00:16, Vincent Guittot 写道:
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@xxxxxxxxxx>
Reviewed-and-tested-by: Lukasz Luba <lukasz.luba@xxxxxxx>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Reviewed-by: Hongyan Xia <hongyan.xia2@xxxxxxx>
Reviewed-by: Tang Yizhou <yizhou.tang@xxxxxxxxxx>

For Chinese translation,


Reviewed-by: Yanteng Si <siyanteng@xxxxxxxxxxx>


Thanks,

Yanteng

---
  Documentation/scheduler/schedutil.rst                    | 7 +++----
  Documentation/translations/zh_CN/scheduler/schedutil.rst | 7 +++----
  kernel/sched/fair.c                                      | 8 +++-----
  kernel/sched/features.h                                  | 1 -
  4 files changed, 9 insertions(+), 14 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/Documentation/translations/zh_CN/scheduler/schedutil.rst b/Documentation/translations/zh_CN/scheduler/schedutil.rst
index d1ea68007520..7c8d87f21c42 100644
--- a/Documentation/translations/zh_CN/scheduler/schedutil.rst
+++ b/Documentation/translations/zh_CN/scheduler/schedutil.rst
@@ -89,16 +89,15 @@ r_cpu被定义为当前CPU的最高性能水平与系统中任何其它CPU的最
   - Documentation/translations/zh_CN/scheduler/sched-capacity.rst:"1. CPU Capacity + 2. Task utilization"
-UTIL_EST / UTIL_EST_FASTUP
-==========================
+UTIL_EST
+========
由于周期性任务的平均数在睡眠时会衰减,而在运行时其预期利用率会和睡眠前相同,
  因此它们在再次运行后会面临(DVFS)的上涨。
为了缓解这个问题,(一个默认使能的编译选项)UTIL_EST驱动一个无限脉冲响应
  (Infinite Impulse Response,IIR)的EWMA,“运行”值在出队时是最高的。
-另一个默认使能的编译选项UTIL_EST_FASTUP修改了IIR滤波器,使其允许立即增加,
-仅在利用率下降时衰减。
+UTIL_EST滤波使其在遇到更高值时立刻增加,而遇到低值时会缓慢衰减。
进一步,运行队列的(可运行任务的)利用率之和由下式计算: diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bcea3d55d95d..e94d65da8d66 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)





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