From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S932394Ab1AKRKy (ORCPT <rfc822;w@1wt.eu>);
	Tue, 11 Jan 2011 12:10:54 -0500
Received: from e23smtp03.au.ibm.com ([202.81.31.145]:41992 "EHLO
	e23smtp03.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1753020Ab1AKRKw (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 11 Jan 2011 12:10:52 -0500
Date: Tue, 11 Jan 2011 22:40:46 +0530
From: Bharata B Rao <bharata@linux.vnet.ibm.com>
To: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, Ingo Molnar <mingo@elte.hu>,
        linux-kernel@vger.kernel.org
Subject: Re: [patch] Re: autogroup: sched_setscheduler() fails
Message-ID: <20110111171046.GL4772@in.ibm.com>
Reply-To: bharata@linux.vnet.ibm.com
References: <20110110091622.GF2772@in.ibm.com>
 <1294655388.8197.22.camel@marge.simson.net>
 <1294657154.2016.459.camel@laptop>
 <1294677746.8345.4.camel@marge.simson.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1294677746.8345.4.camel@marge.simson.net>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

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.