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

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Message-Id: <20240725114200.375611-1-yu.c.chen@intel.com>
Date: Thu, 25 Jul 2024 19:42:00 +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: Qais Yousef <qyousef@...alina.io>,
	Lukasz Luba <lukasz.luba@....com>,
	linux-kernel@...r.kernel.org,
	Chen Yu <yu.c.chen@...el.com>,
	kernel test robot <oliver.sang@...el.com>
Subject: [PATCH] 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. While looking at a related
bug report, it is found that this commit uses the sched_clock_task()
in sched_tick() while 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. Although this should not impact x86 platform in the bug report,
it should be fixed for other platforms.

Fixes: 97450eb90965 ("sched/pelt: Remove shift of thermal clock")
Reported-by: kernel test robot <oliver.sang@...el.com>
Closes: https://lore.kernel.org/oe-lkp/202407091527.bb0be229-lkp@intel.com
Signed-off-by: Chen Yu <yu.c.chen@...el.com>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9057584ec06d..cfd4755954fd 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_clock_task(rq), rq, hw_pressure) |
 		  update_irq_load_avg(rq, 0);

 	if (others_have_blocked(rq))
-- 
2.25.1