From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756566AbZCLV3z (ORCPT ); Thu, 12 Mar 2009 17:29:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751638AbZCLV3r (ORCPT ); Thu, 12 Mar 2009 17:29:47 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:34880 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750809AbZCLV3q (ORCPT ); Thu, 12 Mar 2009 17:29:46 -0400 Message-ID: <49B97EC5.9050109@us.ibm.com> Date: Thu, 12 Mar 2009 14:29:41 -0700 From: Darren Hart User-Agent: Thunderbird 2.0.0.19 (X11/20090105) MIME-Version: 1.0 To: Peter Zijlstra CC: Arjan van de Ven , mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, rusty@rustcorp.com.au, tglx@linutronix.de, mingo@elte.hu, linux-tip-commits@vger.kernel.org Subject: Re: [tip:core/futexes] futex: use current->time_slack_ns for rt tasks too References: <20090312075559.9856.28822.stgit@Aeon> <49B913DC.6040807@linux.intel.com> <1236866529.22914.3694.camel@twins> In-Reply-To: <1236866529.22914.3694.camel@twins> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter Zijlstra wrote: > On Thu, 2009-03-12 at 06:53 -0700, Arjan van de Ven wrote: >> Darren Hart wrote: >>> Commit-ID: 16f4993f4e9860715918efd4eeac928f8de1218b >>> Gitweb: http://git.kernel.org/tip/16f4993f4e9860715918efd4eeac928f8de1218b >>> Author: "Darren Hart" >>> AuthorDate: Thu, 12 Mar 2009 00:55:59 -0700 >>> Commit: Ingo Molnar >>> CommitDate: Thu, 12 Mar 2009 11:20:57 +0100 >>> >>> futex: use current->time_slack_ns for rt tasks too >>> >>> RT tasks should set their timer slack to 0 on their own. This >>> patch removes the 'if (rt_task()) slack = 0;' block in >>> futex_wait. >> Hi, >> >> can you explain the rationale for this reasoning? > > Yeah, I found it iffy as well, I think we want something like the below > instead though.. > > --- > > Subject: sched: adjust timer_slack_ns on scheduler policy change > From: Peter Zijlstra > Date: Thu Mar 12 15:01:02 CET 2009 > > Ensure RT tasks have 0 timer slack. Fork takes care of this by setting the child's default_timer_slack_ns to current->timer_slack_ns. This change takes care of tasks that are converted to rt by the user. What about tasks that are demoted from RT to SCHED_NORMAL? I'm not sure setting it to the default_timer_slack_ns is the right thing since that could have been the timer_slack_ns of the rt process it forked from. Perhaps heach scheduler class needs to have a default_timer_slack_ns set in the class? > > Signed-off-by: Peter Zijlstra > --- > kernel/sched.c | 2 ++ > 1 file changed, 2 insertions(+) > > Index: linux-2.6/kernel/sched.c > =================================================================== > --- linux-2.6.orig/kernel/sched.c > +++ linux-2.6/kernel/sched.c > @@ -5511,10 +5511,12 @@ __setscheduler(struct rq *rq, struct tas > case SCHED_NORMAL: > case SCHED_BATCH: > case SCHED_IDLE: > + p->timer_slack_ns = p->default_timer_slack_ns; > p->sched_class = &fair_sched_class; > break; > case SCHED_FIFO: > case SCHED_RR: > + p->timer_slack_ns = 0; > p->sched_class = &rt_sched_class; > break; > } > -- Darren Hart IBM Linux Technology Center Real-Time Linux Team