[tip: sched/core] sched/pelt: Use rq_clock_task() for hw_pressure

[tip-bot2 for Chen Yu]

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

Commit-ID:     84d265281d6cea65353fc24146280e0d86ac50cb
Gitweb:        https://git.kernel.org/tip/84d265281d6cea65353fc24146280e0d86ac50cb
Author:        Chen Yu <yu.c.chen@xxxxxxxxx>
AuthorDate:    Tue, 27 Aug 2024 19:26:07 +08:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 10 Sep 2024 09:51:14 +02:00

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.

Fixes: 97450eb90965 ("sched/pelt: Remove shift of thermal clock")
Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Hongyan Xia <hongyan.xia2@xxxxxxx>
Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20240827112607.181206-1-yu.c.chen@xxxxxxxxx
---
 kernel/sched/fair.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9e19009..e946ca0 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9719,9 +9719,10 @@ static bool __update_blocked_others(struct rq *rq, bool *done)
 
 	hw_pressure = arch_scale_hw_pressure(cpu_of(rq));
 
+	/* hw_pressure doesn't care about invariance */
 	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))