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

Dietmar Eggemann
2021-07-30T12:22:22Z

On 29/07/2021 16:38, Dietmar Eggemann wrote:
> On 29/07/2021 14:36, Bruno Goncalves wrote:
>> On Wed, Jul 28, 2021 at 5:55 PM Dietmar Eggemann
>> <dietmar.eggemann@arm.com> wrote:
>>>
>>> On 28/07/2021 15:11, Bruno Goncalves wrote:
>
> [...]
>
>>> 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