Changing RT task to a different cgroup

I would try the cgroups mailing list:

http://vger.kernel.org/vger-lists.html#cgroups

Juan.

On Tue, Sep 20, 2016 at 2:39 PM, Rahul Bhattacharya
[off-list ref] wrote:

Any idea or feedback for the person to contact?
Thanks

br
rb

On Wed, Sep 14, 2016 at 5:21 PM, Rahul Bhattacharya [off-list ref]
wrote:

quoted

When I try to move a RT task to a different cgroup(shown below) I get a
EINVAL error.

However I can change the cgroup first and then change the sched policy.

After looking into kernel source code(I dont use CONFIG_RT_GROUP_SCHED
config) I was able to extract this piece of logic



chrt -p 777
pid 777's current scheduling policy: SCHED_OTHER
pid 777's current scheduling priority: 0

cat /proc/777/cgroup
2:cpu,cpuacct:/system.slice
1:name=systemd:/system.slice/d.service

chrt -f -p 50 777

root at mgu-high:~# chrt -p 777
pid 777's current scheduling policy: SCHED_FIFO
pid 777's current scheduling priority: 50

/bin/echo 777>/sys/fs/cgroup/cpu,cpuacct/interaction.slice/tasks
echo: write error: Invalid argument



After browsing kernel sources I was able to find out the reason of
failure.


static int cpu_cgroup_can_attach(struct cgroup_subsys_state *css,
				 struct cgroup_taskset *tset)
{
	struct task_struct *task;

		
	cgroup_taskset_for_each(task, tset) {
#ifdef CONFIG_RT_GROUP_SCHED
		if (!sched_rt_can_attach(css_tg(css), task))
			return -EINVAL;
#else
		/* We don't support RT-tasks being in separate groups */
		if (task->sched_class != &fair_sched_class)
		{
			return -EINVAL;
		}
#endif
	}
	return 0;
}

My question is why is this check required? Also, changing cgroups first
and then the policy of FIFO works without issue(?) for the task.

Thanks


br

rb

_______________________________________________
Kernelnewbies mailing list
Kernelnewbies at kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

-- 
Juan-Luis de Sousa-Valadas Casta?o
Iberia Infrastructure Consultant - Red Hat