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

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

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.