From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752674Ab1ALGR7 (ORCPT ); Wed, 12 Jan 2011 01:17:59 -0500 Received: from mailout-de.gmx.net ([213.165.64.23]:53563 "HELO mail.gmx.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with SMTP id S1751405Ab1ALGR5 (ORCPT ); Wed, 12 Jan 2011 01:17:57 -0500 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX1/ggitQGfrgatpNg8yDTXHCoH9xsB2ixaOkDKnB5h JS+UgZbf0DrMNC Subject: Re: [patch] Re: autogroup: sched_setscheduler() fails From: Mike Galbraith To: bharata@linux.vnet.ibm.com Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org In-Reply-To: <20110112033709.GA2723@in.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> <20110111171046.GL4772@in.ibm.com> <1294771686.8006.15.camel@marge.simson.net> <20110112033709.GA2723@in.ibm.com> Content-Type: text/plain; charset="UTF-8" Date: Wed, 12 Jan 2011 07:17:52 +0100 Message-ID: <1294813072.8370.24.camel@marge.simson.net> Mime-Version: 1.0 X-Mailer: Evolution 2.30.1.2 Content-Transfer-Encoding: 7bit X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2011-01-12 at 09:07 +0530, Bharata B Rao wrote: > On Tue, Jan 11, 2011 at 07:48:06PM +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//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. > > Ok, this is what I understand, may be Peter Z can confirm... > > set_task_rq() just changes the task's cfs_rq and rt_rq as per its > task_group(). Exactly. When you call task_group() for an RT task, it returns &root_task_group, so a task making the transition to RT will be dequeued from it's autogroup cfs_rq, and enqueued in root_task_group's rt_rq. > The normal way to change a task's group is to first > change its cgroup pointer (task->cgroups, see cgroup_attach_task()) > After this you change the runqueues by calling set_task_rq() which > now refers to new group's runqueues. Autogroup doesn't need to do cgroup stuff. If a task is in a cgroup, it's autogroup remains intact, but is ignored. Move it back to root, and it's autogroup will be used again. -Mike