From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752332AbYKXIc2 (ORCPT ); Mon, 24 Nov 2008 03:32:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751133AbYKXIcU (ORCPT ); Mon, 24 Nov 2008 03:32:20 -0500 Received: from viefep11-int.chello.at ([62.179.121.31]:61738 "EHLO viefep11-int.chello.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751029AbYKXIcU (ORCPT ); Mon, 24 Nov 2008 03:32:20 -0500 X-SourceIP: 213.46.9.244 Subject: Re: [PATCH] sched: Don't allow priority switch to realtime when the task doesn't belong to init_task_group and when CONFIG_RT_GROUP_SCHED isn't set From: Peter Zijlstra To: bharata@linux.vnet.ibm.com Cc: linux-kernel@vger.kernel.org, Srivatsa Vaddagiri , Ingo Molnar , Dhaval Giani In-Reply-To: <20081124035807.GA3278@in.ibm.com> References: <20081120061854.GA4349@in.ibm.com> <1227402676.7685.19942.camel@twins> <20081124035807.GA3278@in.ibm.com> Content-Type: text/plain Date: Mon, 24 Nov 2008 09:32:06 +0100 Message-Id: <1227515526.7685.21861.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.24.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2008-11-24 at 09:28 +0530, Bharata B Rao wrote: > On Sun, Nov 23, 2008 at 02:11:16AM +0100, Peter Zijlstra wrote: > > On Thu, 2008-11-20 at 11:48 +0530, Bharata B Rao wrote: > > > Applies on 2.6.28-rc5. > > > > > > With CONFIG_RT_GROUP_SCHED not set, don't allow a task's priority switch > > > to realtime if the task isn't part of init_task_group. > > > > > > A task belonging to a fair group could use sched_setscheduler/sched_setparam > > > to become a realtime task. If such a task belongs to one of the > > > child groups of init_task_group and if CONFIG_RT_GROUP_SCHED is not set, > > > then it ends up getting queued in init_task_group's runqueue. > > > So we have a situation where, a task belongs to one group (child) > > > but ends in the runqueue of another group (init_task_group). > > > This does not look correct. > > > > > > Fix this by failing such priority change requests in sched_setscheduler() > > > and sched_setparam(). > > > > NAK > > > > !RT_GROUP means the RT tasks should be fully invariant to any grouping > > configuration. This patch breaks that. > > > > Furthermore your justification for this is plain wrong, you write as if > > an RT tasks can belong to any grouping (in the !RT_GROUP case), by the > > Hmm... but that's I the impression I got when I started an RT > task in a subgroup and saw it listed in the tasks list of the cgroup. > So if RT tasks don't care about grouping (!RT_GROUP_SCHED), may be then > such tasks shoudn't be shown in the cgroup tasks list. Sure, do as you like upon the cgroup interface > And may be as Ingo > suggested they should be moved to init_task_group. Bzzt, wrong! They should not be moved to any group, they cannot be moved to any group, as they are group invariant. > Without that it makes one > think that a task is contributing to the cpu time of a group in which > it was started, but it in reality it is not. Until one thinks more and realizes RT tasks don't contribute anything to groups as they are not part of them.