Re: [Question] Sched: Severe scheduling latency (>10s) observed on kernel 6.12 with specific workload

[Dietmar Eggemann <dietmar.eggemann@arm.com>]

On 08.04.26 03:50, Xuewen Yan wrote:
> Hi Dietmar and Vincent,
> 
>> I tried to recreate your env as much as possible on qemu and ran your
>> rt-app file but I can't spot anything suspicious either. This is with
>> defconfig and cgroupv2.
> 
> Could you please try the following configuration?
> To rule out Android's influence, I created two new cgroups:
> foreground_test and background_test.
> I then placed only rt-app threads into these groups. Even with this
> setup, we can still observe high scheduling latency for tasks in
> foreground_test.

Is this still on an Android (vendor hooks, etc.) or mainline 6.12.58
kernel/device?

> {
>     "tasks" : {
>             "t0" : {
>                     "instance" : 40,
>                     "priority" : 0,
>                     "cpus" : [ 0, 1, 2, 3 ],
> "taskgroup" : "/background_test",
>                     "loop" : -1,
>                     "run" : 200,
>                     "sleep" : 50
>             },
> "t1" : {
>                     "instance" : 2,
>                     "priority" : 19,
>                     "cpus" : [ 0, 1, 2, 3 ],
> "taskgroup" : "/foreground_test",
>                     "loop" : -1,
>                     "run" : 60000,
>                     "sleep" : 100000
>             },
> "t2" : {
>                     "instance" : 2,
>                     "priority" : 10,
>                     "cpus" : [ 0, 1, 2, 3 ],
> "taskgroup" : "/foreground_test",
>                     "loop" : -1,
>                     "run" : 5000,
>                     "sleep" : 100000
>             }
>     }
> }

With your rt-app file and moving the tasks into cgroupv2 taskgroups
manually:

t0-0 679 0 > /sys/fs/cgroup/A
t0-1 680 0 > /sys/fs/cgroup/A
t0-2 681 0 > /sys/fs/cgroup/A
...
t0-37 716 0 > /sys/fs/cgroup/A
t0-38 717 0 > /sys/fs/cgroup/A
t0-39 718 0 > /sys/fs/cgroup/A
t1-40 719 19 > /sys/fs/cgroup/B
t1-41 720 19 > /sys/fs/cgroup/B
t2-42 721 10 > /sys/fs/cgroup/B
t2-43 722 10 > /sys/fs/cgroup/B

10 highest wu_lat values on Arm64 qemu (-accel hvf):

v6.6

0.564159000 t2-43:684
0.306418000 t2-42:683
0.237134000 t2-43:684
0.166982000 t2-42:683
0.166674000 t2-42:683
0.161856000 t2-42:683
0.098879000 t2-43:684
0.097746000 t2-43:684
0.083329000 t2-42:683
0.082943000 t2-42:683

6.12.58

0.368566000 t2-43:939
0.228139000 t2-42:938
0.212454000 t2-43:939
0.207144000 t2-42:938
0.177373000 t2-43:939
0.148268000 t2-42:938
0.147619000 t2-42:938
0.125988000 t2-43:939
0.091564000 t2-42:938
0.088160000 t2-42:938

tip sched/core (7.0.0-rc6-00050-g985215804dcb)

0.395585000 t2-43:697
0.203889000 t2-43:697
0.101130000 t2-42:696
0.098782000 t2-42:696
0.084523000 t2-43:697
0.033895000 t2-42:696
0.031881000 t2-43:697
0.021958000 t2-42:696
0.018123000 t2-42:696
0.013132000 t0-7:661

Could you specify which tasks had those > 1s wu_lat values?