From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758907AbcKCQ7k (ORCPT ); Thu, 3 Nov 2016 12:59:40 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:45963 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754015AbcKCQ7i (ORCPT ); Thu, 3 Nov 2016 12:59:38 -0400 Date: Thu, 3 Nov 2016 09:59:31 -0700 From: "Paul E. McKenney" To: Sebastian Andrzej Siewior Cc: "Michael S. Tsirkin" , Julia Cartwright , Luiz Capitulino , linux-rt-users@vger.kernel.org, Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , linux-kernel@vger.kernel.org Subject: Re: [PATCH] rcu: update: make RCU_EXPEDITE_BOOT default Reply-To: paulmck@linux.vnet.ibm.com References: <20161012203223.GK29518@linux.vnet.ibm.com> <20161013191332-mutt-send-email-mst@kernel.org> <20161014092050.GW29518@linux.vnet.ibm.com> <20161016044420-mutt-send-email-mst@kernel.org> <20161016112846.GR29518@linux.vnet.ibm.com> <20161031173852.a3ji7hhgjis5l3u4@linutronix.de> <20161031181543.GN3716@linux.vnet.ibm.com> <20161102163002.igni3zdnid535nou@linutronix.de> <20161103162228.GG3716@linux.vnet.ibm.com> <20161103163326.jkjbncoz7a5oriy5@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20161103163326.jkjbncoz7a5oriy5@linutronix.de> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16110316-0004-0000-0000-000010C26896 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006026; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000189; SDB=6.00776298; UDB=6.00373407; IPR=6.00553456; BA=6.00004855; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013202; XFM=3.00000011; UTC=2016-11-03 16:59:34 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16110316-0005-0000-0000-00007A45C720 Message-Id: <20161103165931.GJ3716@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-11-03_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1609300000 definitions=main-1611030315 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 03, 2016 at 05:33:27PM +0100, Sebastian Andrzej Siewior wrote: > On 2016-11-03 09:22:28 [-0700], Paul E. McKenney wrote: > > On Wed, Nov 02, 2016 at 05:30:02PM +0100, Sebastian Andrzej Siewior wrote: > > > RCU_EXPEDITE_BOOT should speed up the boot process by enforcing > > > synchronize_rcu_expedited() instead of synchronize_rcu() during the boot > > > process. There should be no reason why one does not want this and there > > > is no need worry about real time latency at this point. > > > Therefore make it default. > > > > > > Signed-off-by: Sebastian Andrzej Siewior > > > > Well, it has been awhile since I removed a Kconfig parameter. > > > > So why could this be a bad thing? > > > > 1. Very large systems might see scalability issues with unconditional > > expediting at boot. But if we don't try it, we won't know. > > You mean we would make the boot process slower for them instead of > faster? For really bit systems, quite possibly, where "really big" means many hundreds or (more likely) thousands of CPUs. But there are things that I can do to fix this when and if. > > 2. People bringing up new hardware might not want quite so many > > IPIs. But they can just set rcu_normal to prevent that. > > I wanted to make things simple and not complicated… I know that feeling. ;-) > > I am therefore queuing it for testiong and review. ;-) > > Okay thanks. Thanx, Paul > Sebastian >