From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756787AbZCLODY (ORCPT ); Thu, 12 Mar 2009 10:03:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755296AbZCLODM (ORCPT ); Thu, 12 Mar 2009 10:03:12 -0400 Received: from casper.infradead.org ([85.118.1.10]:53613 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754692AbZCLODK (ORCPT ); Thu, 12 Mar 2009 10:03:10 -0400 Subject: Re: [tip:core/futexes] futex: use current->time_slack_ns for rt tasks too From: Peter Zijlstra To: Arjan van de Ven Cc: mingo@redhat.com, hpa@zytor.com, dvhltc@us.ibm.com, linux-kernel@vger.kernel.org, rusty@rustcorp.com.au, tglx@linutronix.de, mingo@elte.hu, linux-tip-commits@vger.kernel.org In-Reply-To: <49B913DC.6040807@linux.intel.com> References: <20090312075559.9856.28822.stgit@Aeon> <49B913DC.6040807@linux.intel.com> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Thu, 12 Mar 2009 15:02:09 +0100 Message-Id: <1236866529.22914.3694.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.24.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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; }