Re: SCHED_DEADLINE tasks missing their deadline with SCHED_FLAG_RECLAIM jobs in the mix (using GRUB)

luca abeni
2025-05-23T19:46:12Z

Hi Marcel,

sorry, but I have some additional questions to fully understand your
setup...

On Mon, 19 May 2025 15:32:27 +0200
Marcel Ziswiler <marcel.ziswiler@codethink.co.uk> wrote:
[...]
> > just a quick question to better understand your setup (and check
> > where the issue comes from):
> > in the email below, you say that tasks are statically assigned to
> > cores; how did you do this? Did you use isolated cpusets,
>
> Yes, we use the cpuset controller from the cgroup-v2 APIs in the
> linux kernel in order to partition CPUs and memory nodes. In detail,
> we use the AllowedCPUs and AllowedMemoryNodes in systemd's slice
> configurations.

How do you configure systemd? I am having troubles in reproducing your
AllowedCPUs configuration... This is an example of what I am trying:
sudo systemctl set-property --runtime custom-workload.slice AllowedCPUs=1
sudo systemctl set-property --runtime init.scope AllowedCPUs=0,2,3
sudo systemctl set-property --runtime system.slice AllowedCPUs=0,2,3
sudo systemctl set-property --runtime user.slice AllowedCPUs=0,2,3
and then I try to run a SCHED_DEADLINE application with
sudo systemd-run --scope -p Slice=custom-workload.slice <application>

However, this does not work because systemd is not creating an isolated
cpuset... So, the root domain still contains CPUs 0-3, and the
"custom-workload.slice" cpuset only has CPU 1. Hence, the check
/*
* Don't allow tasks with an affinity mask smaller than
* the entire root_domain to become SCHED_DEADLINE. We
* will also fail if there's no bandwidth available.
*/
if (!cpumask_subset(span, p->cpus_ptr) ||
rq->rd->dl_bw.bw == 0) {
retval = -EPERM;
goto unlock;
}
in sched_setsched() fails.

How are you configuring the cpusets? Also, which kernel version are you using?
(sorry if you already posted this information in previous emails and I am
missing something obvious)

Thanks,
Luca