From mboxrd@z Thu Jan  1 00:00:00 1970
From: Clark Williams <williams@redhat.com>
Subject: Re: cyclictest: Unable to set scheduling policy / join real-time
 group or run as root
Date: Wed, 27 Feb 2013 10:09:57 -0600
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Cc: linux-rt-users@vger.kernel.org
To: Hartmut Behrens <hartmut.behrens@gmail.com>
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On Wed, 27 Feb 2013 08:26:45 +0200
Hartmut Behrens <hartmut.behrens@gmail.com> wrote:

> On Mon, Feb 25, 2013 at 11:21 PM, Clark Williams <williams@redhat.com> wr=
ote:
> > Changing your scheduling policy requires extra privileges. You can
> > either run cyclictest as root, or if your distribution uses PAM, you
> > can set up a file in /etc/security/limits.d which enable group access to
> > changing scheduler policy. You can name the file whatever you want, I
> > usually call mine 99-realtime.conf:
> >
> > # cat <<EOF >/etc/security/limits.d/99-realtime.conf
> > @realtime       -       rtprio  99
> > @realtime       -       memlock unlimited
> > EOF
> >
> > Then create a group named realtime and add your username to the newly
> > created group:
> >
> > # groupadd realtime
> > # usermod -a -G realtime yourUserID
> >
> > Log out, then log back in and you should be able to verift that you're
> > in the realtime group using the 'groups' command. Once you're username
> > is a member of the realtime group, you should be able to run cyclictest
> > without being root.
>=20
> This problem persists even when I run cyclictest as root. I have also
> set up PAM as described above and added root to the realtime group
> without any success.
> I have also tried "sudo ./cyclictest" and " su -c './cyclictest'
>=20
> Is this perhaps a more fundamental problem?
>=20
> Just to recap: I applied the patch-3.2-rt10 patch cleanly to a v3.2
> kernel customized for a TI OMAP (ARM) processor. CONFIG_PREEMPT_RT was
> enabled and CPU frequency scaling disabled.
>=20

This shouldn't have anything to do with the PREEMPT_RT patchset.
Changing scheduling policy via the sched_setscheduler(2) syscall is a
fundamental component of the Linux scheduler.=20

What happens if you compile and run this program on your kernel?
#include <stdio.h>
#include <stdlib.h>
#include <sched.h>
#include <errno.h>
#include <memory.h>

int main(int argc, char **argv)
{
	int ret;
	struct sched_param s;

	memset(&s, 0, sizeof(s));
	s.sched_priority =3D 1;
	if ((sched_setscheduler(0, SCHED_FIFO, &s))) {
		fprintf(stderr, "error changing policy: %s\n", strerror(errno));
		exit(errno);
	}
	printf("successfully changed policy to SCHED_FIFO priority 1\n");
	exit(0);
}

Clark

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