linux-kernel - [PATCH v3] sched/pelt: Use rq_clock_task() for hw

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Message-Id: <20240729070029.407884-1-yu.c.chen@intel.com>
Date: Mon, 29 Jul 2024 15:00:29 +0800
From: Chen Yu <yu.c.chen@...el.com>
To: Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Juri Lelli <juri.lelli@...hat.com>
Cc: Hongyan Xia <hongyan.xia2@....com>,
	Qais Yousef <qyousef@...alina.io>,
	Lukasz Luba <lukasz.luba@....com>,
	linux-kernel@...r.kernel.org,
	Chen Yu <yu.c.chen@...el.com>
Subject: [PATCH v3] sched/pelt: Use rq_clock_task() for hw_pressure

commit 97450eb90965 ("sched/pelt: Remove shift of thermal clock")
removed the decay_shift for hw_pressure. This commit uses the
sched_clock_task() in sched_tick() while it replaces the
sched_clock_task() with rq_clock_pelt() in __update_blocked_others().
This could bring inconsistence. One possible scenario I can think of
is in ___update_load_sum():

u64 delta = now - sa->last_update_time

'now' could be calculated by rq_clock_pelt() from
__update_blocked_others(), and last_update_time was calculated by
rq_clock_task() previously from sched_tick(). Usually the former
chases after the latter, it cause a very large 'delta' and brings
unexpected behavior.

Fix this by using rq_clock_task() inside update_hw_load_avg(),
because:
1. hw_pressure doesn't care about invariance.
2. avoid any inconsistence in the future.

Fixes: 97450eb90965 ("sched/pelt: Remove shift of thermal clock")
Suggested-by: Qais Yousef <qyousef@...alina.io>
Reviewed-by: Hongyan Xia <hongyan.xia2@....com>
Signed-off-by: Chen Yu <yu.c.chen@...el.com>
---
v2>v3:
  call rq_clock_task() inside update_hw_load_avg() to avoid any
  inconsistence in the future. (Qais Yousef)
  Added comments around update_hw_load_avg(). (Qais Yousef)
v1->v2:
  Added Hongyan's Reviewed-by tag.
  Removed the Reported-by/Closes tags because they are not related
  to this fix.(Hongyan Xia)
---
 kernel/sched/core.c | 2 +-
 kernel/sched/fair.c | 2 +-
 kernel/sched/pelt.c | 5 +++--
 kernel/sched/pelt.h | 6 +++---
 4 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a9f655025607..011d447e065f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5462,7 +5462,7 @@ void sched_tick(void)
 
 	update_rq_clock(rq);
 	hw_pressure = arch_scale_hw_pressure(cpu_of(rq));
-	update_hw_load_avg(rq_clock_task(rq), rq, hw_pressure);
+	update_hw_load_avg(rq, hw_pressure);
 	curr->sched_class->task_tick(rq, curr, 0);
 	if (sched_feat(LATENCY_WARN))
 		resched_latency = cpu_resched_latency(rq);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9057584ec06d..193ac2c702d9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9362,7 +9362,7 @@ static bool __update_blocked_others(struct rq *rq, bool *done)
 
 	decayed = update_rt_rq_load_avg(now, rq, curr_class == &rt_sched_class) |
 		  update_dl_rq_load_avg(now, rq, curr_class == &dl_sched_class) |
-		  update_hw_load_avg(now, rq, hw_pressure) |
+		  update_hw_load_avg(rq, hw_pressure) |
 		  update_irq_load_avg(rq, 0);
 
 	if (others_have_blocked(rq))
diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
index fa52906a4478..06a5fa85327c 100644
--- a/kernel/sched/pelt.c
+++ b/kernel/sched/pelt.c
@@ -400,9 +400,10 @@ int update_dl_rq_load_avg(u64 now, struct rq *rq, int running)
  *			capped capacity a cpu due to a HW event.
  */
 
-int update_hw_load_avg(u64 now, struct rq *rq, u64 capacity)
+int update_hw_load_avg(struct rq *rq, u64 capacity)
 {
-	if (___update_load_sum(now, &rq->avg_hw,
+	/* hw_pressure doesn't care about invariance */
+	if (___update_load_sum(rq_clock_task(rq), &rq->avg_hw,
 			       capacity,
 			       capacity,
 			       capacity)) {
diff --git a/kernel/sched/pelt.h b/kernel/sched/pelt.h
index 2150062949d4..261172c29f8f 100644
--- a/kernel/sched/pelt.h
+++ b/kernel/sched/pelt.h
@@ -8,7 +8,7 @@ int update_rt_rq_load_avg(u64 now, struct rq *rq, int running);
 int update_dl_rq_load_avg(u64 now, struct rq *rq, int running);
 
 #ifdef CONFIG_SCHED_HW_PRESSURE
-int update_hw_load_avg(u64 now, struct rq *rq, u64 capacity);
+int update_hw_load_avg(struct rq *rq, u64 capacity);
 
 static inline u64 hw_load_avg(struct rq *rq)
 {
@@ -16,7 +16,7 @@ static inline u64 hw_load_avg(struct rq *rq)
 }
 #else
 static inline int
-update_hw_load_avg(u64 now, struct rq *rq, u64 capacity)
+update_hw_load_avg(struct rq *rq, u64 capacity)
 {
 	return 0;
 }
@@ -202,7 +202,7 @@ update_dl_rq_load_avg(u64 now, struct rq *rq, int running)
 }
 
 static inline int
-update_hw_load_avg(u64 now, struct rq *rq, u64 capacity)
+update_hw_load_avg(struct rq *rq, u64 capacity)
 {
 	return 0;
 }
-- 
2.25.1