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SubjectRe: [patch] Re: autogroup: sched_setscheduler() fails
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On Tue, 2011-01-11 at 19:48 +0100, Mike Galbraith wrote:
> On Tue, 2011-01-11 at 22:40 +0530, Bharata B Rao wrote:
> > On Mon, Jan 10, 2011 at 05:42:26PM +0100, Mike Galbraith wrote:
> > > Index: linux-2.6/kernel/sched_autogroup.c
> > > ===================================================================
> > > --- linux-2.6.orig/kernel/sched_autogroup.c
> > > +++ linux-2.6/kernel/sched_autogroup.c
> > > @@ -73,6 +73,15 @@ static inline struct autogroup *autogrou
> > > ag->id = atomic_inc_return(&autogroup_seq_nr);
> > > ag->tg = tg;
> > > tg->autogroup = ag;
> > > +#ifdef CONFIG_RT_GROUP_SCHED
> > > + /*
> > > + * HACK: autogroup RT tasks run in the root task group.
> > > + * This fools __sched_setscheduler() into proceeding on
> > > + * so we can move the task to the appropriate runqueue
> > > + * upon scheduling policy change.
> > > + */
> > > + tg->rt_bandwidth.rt_runtime = RUNTIME_INF;
> > > +#endif
> > >
> > > return ag;
> > >
> > > @@ -143,6 +152,15 @@ autogroup_move_group(struct task_struct
> > > autogroup_kref_put(prev);
> > > }
> > >
> > > +static inline void
> > > +autogroup_setscheduler(struct task_struct *p, int on_rq)
> > > +{
> > > + if (p->sched_class->task_move_group)
> > > + p->sched_class->task_move_group(p, on_rq);
> > > + else
> > > + set_task_rq(p, task_cpu(p));
> > > +}
> > > +
> >
> > IIUC, with the above changes you are actually queing the task into
> > rt_rq of an autogroup. But the task's autogroup interface
> > (/proc/<pid>/autogroup) allows you to control the bandwidth of only
> > cfs_rq tasks, while the rt tasks in the group get RUNTIME_INF bandwidth.
> >
> > I think what we need is a real group change here (which is difficult I
> > think) and not just sched_class change.
>
> Unless I fscked up, set_task_rq() is the group change. As soon as the
> task's class changes, it'll be moved to the root_task_group.

But it'd be better to not touch anything, just deflect RT tasks away
from useless queues from the start.

sched, autogroup: fix CONFIG_RT_GROUP_SCHED sched_setscheduler() failure.

If CONFIG_RT_GROUP_SCHED is set, sched_setscheduler() fails due to autogroup
not allocating rt_runtime. Squirrel allocated but useless rt_se and rt_rq
away for group destruction time, and deflect RT tasks to the root task group.

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

---
kernel/sched_autogroup.c | 13 +++++++++++++
kernel/sched_autogroup.h | 4 ++++
2 files changed, 17 insertions(+)

Index: linux-2.6/kernel/sched_autogroup.c
===================================================================
--- linux-2.6.orig/kernel/sched_autogroup.c
+++ linux-2.6/kernel/sched_autogroup.c
@@ -27,6 +27,11 @@ static inline void autogroup_destroy(str
{
struct autogroup *ag = container_of(kref, struct autogroup, kref);

+#ifdef CONFIG_RT_GROUP_SCHED
+ ag->tg->rt_se = ag->rt_se;
+ ag->tg->rt_rq = ag->rt_rq;
+ ag->tg->rt_bandwidth.rt_runtime = 0;
+#endif
sched_destroy_group(ag->tg);
}

@@ -72,6 +77,14 @@ static inline struct autogroup *autogrou
init_rwsem(&ag->lock);
ag->id = atomic_inc_return(&autogroup_seq_nr);
ag->tg = tg;
+#ifdef CONFIG_RT_GROUP_SCHED
+ /* Sorry, we don't do RT, go away. */
+ ag->rt_se = tg->rt_se;
+ ag->rt_rq = tg->rt_rq;
+ tg->rt_se = root_task_group.rt_se;
+ tg->rt_rq = root_task_group.rt_rq;
+ tg->rt_bandwidth.rt_runtime = root_task_group.rt_bandwidth.rt_runtime;
+#endif
tg->autogroup = ag;

return ag;
Index: linux-2.6/kernel/sched_autogroup.h
===================================================================
--- linux-2.6.orig/kernel/sched_autogroup.h
+++ linux-2.6/kernel/sched_autogroup.h
@@ -6,6 +6,10 @@ struct autogroup {
struct rw_semaphore lock;
unsigned long id;
int nice;
+#ifdef CONFIG_RT_GROUP_SCHED
+ struct sched_rt_entity **rt_se;
+ struct rt_rq **rt_rq;
+#endif
};

static inline struct task_group *




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