From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933427AbcKGS3u (ORCPT ); Mon, 7 Nov 2016 13:29:50 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:48482 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933351AbcKGS3k (ORCPT ); Mon, 7 Nov 2016 13:29:40 -0500 Date: Mon, 7 Nov 2016 10:05:13 -0800 From: "Paul E. McKenney" To: Josh Triplett Cc: Sebastian Andrzej Siewior , Steven Rostedt , "Michael S. Tsirkin" , Julia Cartwright , Luiz Capitulino , linux-rt-users@vger.kernel.org, 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: <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> <20161103165931.GJ3716@linux.vnet.ibm.com> <20161107121939.7346923f@gandalf.local.home> <20161107173029.caktxw4piluk5atu@linutronix.de> <20161107173546.t7aokzncidauio43@x> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161107173546.t7aokzncidauio43@x> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16110718-8235-0000-0000-00000990B1ED X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006040; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000189; SDB=6.00777799; UDB=6.00374514; IPR=6.00555115; BA=6.00004861; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013237; XFM=3.00000011; UTC=2016-11-07 18:05:17 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16110718-8236-0000-0000-0000364551EF Message-Id: <20161107180513.GQ24166@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-11-07_08:,, 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-1611070330 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 07, 2016 at 09:35:46AM -0800, Josh Triplett wrote: > On Mon, Nov 07, 2016 at 06:30:30PM +0100, Sebastian Andrzej Siewior wrote: > > On 2016-11-07 12:19:39 [-0500], Steven Rostedt wrote: > > > I agree, but if this creates a boot time regression in large machines, > > > it may not be warranted. > > > > > > I know Linus usually doesn't like options with default y, but this may > > > be one of those exceptions. Perhaps we should make it on by default and > > > say in the config "if you have a machine with 100s or 1000s of CPUs, > > > you may want to disable this". > > > > The default could change if we know where the limit is. I have access to > > a box with approx 140 CPUs so I could check there if it is already bad. > > But everything above that / in the 1000 range is a different story. > > Right; if we can characterize what machines it benefits and what > machines it hurts, we can automatically detect and run the appropriate > case with no configuration option needed. I very much like this approach! Anyone have access to large systems on which this experiment could be carried out? In the absence of new data, I would just set the cutoff at 256 CPUs, as I have done in the past. Thanx, Paul