[patch] Re: autogroup: sched_setscheduler() fails

[Mike Galbraith <efault@gmx.de>]

On Mon, 2011-01-10 at 14:46 +0530, Bharata B Rao wrote:
> Hi,
> 
> With autogroup ON, sched_setscheduler() fails when I try to change the
> scheduling policy of a normal task to either RR or FIFO.
> 
> sched_setscheduler() returns -EPERM when it finds that the group doesn't
> have any rt bandwidth. This is expected because with autogroup, the task
> is in an autogroup for which task_group(p)->rt_bandwidth.rt_runtime is 0.
> 
> I guess the task needs to be moved to appropriate cgroup (from its current
> autogroup) when such policy change is requested, but I wasn't sure if
> group change from sched_setscheduler() can be achieved easily.

Right, autogroup should be excluding CONFIG_RT_GROUP_SCHED, since it
doesn't currently support it.

sched: SCHED_AUTOGROUP selection excludes RT_GROUP_SCHED

Autogroup does not support realtime task groups, so make selection of
SCHED_AUTOGROUP exclude RT_GROUP_SCHED.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Reported-by:Bharata B Rao <bharata@linux.vnet.ibm.com>

---
 init/Kconfig |    5 +++++
 1 file changed, 5 insertions(+)

Index: linux-2.6/init/Kconfig
===================================================================
--- linux-2.6.orig/init/Kconfig
+++ linux-2.6/init/Kconfig
@@ -699,6 +699,7 @@ config RT_GROUP_SCHED
 	bool "Group scheduling for SCHED_RR/FIFO"
 	depends on EXPERIMENTAL
 	depends on CGROUP_SCHED
+	depends on !SCHED_AUTOGROUP
 	default n
 	help
 	  This feature lets you explicitly allocate real CPU bandwidth
@@ -807,6 +808,10 @@ config SCHED_AUTOGROUP
 	  desktop applications.  Task group autogeneration is currently based
 	  upon task session.
 
+	  Note: SCHED_AUTOGROUP does not support realtime tasks, and prevents
+	  enabling RT_GROUP_SCHED.  If you intend to use group scheduling for
+	  realtime tasks, do not enable this option.
+
 config MM_OWNER
 	bool