linux-kernel - Re: SCHED_DEADLINE tasks missing their deadline with SCHED_FLAG

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Message-ID: <20250523214603.043833e3@nowhere>
Date: Fri, 23 May 2025 21:46:03 +0200
From: luca abeni <luca.abeni@...tannapisa.it>
To: Marcel Ziswiler <marcel.ziswiler@...ethink.co.uk>
Cc: Juri Lelli <juri.lelli@...hat.com>, linux-kernel@...r.kernel.org, Ingo
 Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Vineeth
 Pillai	 <vineeth@...byteword.org>
Subject: Re: SCHED_DEADLINE tasks missing their deadline with
 SCHED_FLAG_RECLAIM jobs in the mix (using GRUB)

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@...ethink.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