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SubjectRe: [patch] Re: autogroup: sched_setscheduler() fails
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.

Regards,
Bharata.


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