Re: WARNING: CPU: 112 PID: 2041 at kernel/sched/sched.h:1453

On 29/07/2021 16:38, Dietmar Eggemann wrote:

On 29/07/2021 14:36, Bruno Goncalves wrote:

quoted

On Wed, Jul 28, 2021 at 5:55 PM Dietmar Eggemann
[off-list ref] wrote:

quoted

On 28/07/2021 15:11, Bruno Goncalves wrote:

[...]

quoted

quoted

Can't reproduce it on my Juno (arm64) (slow-switching (scpi-cpufreq
driver)).

We seem to be able to reproduce this only on Ampere Altra machines,
specifically on mtjade and mtsnow cpus.

# cpupower frequency-info
analyzing CPU 0:
  driver: cppc_cpufreq
  CPUs which run at the same hardware frequency: 0
  CPUs which need to have their frequency coordinated by software: 0
  maximum transition latency:  Cannot determine or is not supported.
  hardware limits: 1000 MHz - 2.80 GHz
  available cpufreq governors: conservative ondemand userspace
powersave performance schedutil
  current policy: frequency should be within 2.00 GHz and 2.80 GHz.
                  The governor "schedutil" may decide which speed to use
                  within this range.
  current CPU frequency: 1.55 GHz (asserted by call to hardware)

# ps -eTo comm,pid,pri,class | grep sugov
sugov:0            1082 140 DLN
sugov:1            1085 140 DLN
...
sugov:78           1319 140 DLN
sugov:79           1320 140 DLN

Thanks! In the meantime I got access to an Ampere Altra so I can try
5.14.0-rc1 later today.

The task causing this seem to be the new `cppc_fie` DL task introduced
by commit 1eb5dde674f5 "cpufreq: CPPC: Add support for frequency
invariance" in v5.14-rc1.

With `CONFIG_ACPI_CPPC_CPUFREQ_FIE=y` and schedutil cpufreq governor on
slow-switching system:

DL task curr=`sugov:X` makes p=`cppc_fie` migrate and since it is in
`non_contending` state, migrate_task_rq_dl() calls 

  sub_running_bw()->__sub_running_bw()->cpufreq_update_util()->
  rq_clock()->assert_clock_updated()

on p. 

Can you try this snippet? It should fix it.

--8<--

From: Dietmar Eggemann <dietmar.eggemann@arm.com>
Date: Fri, 30 Jul 2021 14:03:40 +0200
Subject: [PATCH] sched/deadline: Fix missing clock update in
 migrate_task_rq_dl()

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
---
 kernel/sched/deadline.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index aaacd6cfd42f..4920f498492f 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c

@@ -1733,6 +1733,7 @@ static void migrate_task_rq_dl(struct task_struct *p, int new_cpu __maybe_unused
 	 */
 	raw_spin_rq_lock(rq);
 	if (p->dl.dl_non_contending) {
+		update_rq_clock(rq);
 		sub_running_bw(&p->dl, &rq->dl);
 		p->dl.dl_non_contending = 0;
 		/*

-- 
2.25.1

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