Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933159AbcKGRlk (ORCPT ); Mon, 7 Nov 2016 12:41:40 -0500 Received: from slow1-d.mail.gandi.net ([217.70.178.86]:32775 "EHLO slow1-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932380AbcKGRlg (ORCPT ); Mon, 7 Nov 2016 12:41:36 -0500 X-Originating-IP: 50.39.170.172 Date: Mon, 7 Nov 2016 09:35:46 -0800 From: Josh Triplett To: Sebastian Andrzej Siewior Cc: Steven Rostedt , "Paul E. McKenney" , "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 Message-ID: <20161107173546.t7aokzncidauio43@x> References: <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> <20161103165931.GJ3716@linux.vnet.ibm.com> <20161107121939.7346923f@gandalf.local.home> <20161107173029.caktxw4piluk5atu@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161107173029.caktxw4piluk5atu@linutronix.de> User-Agent: NeoMutt/20161014 (1.7.1) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 900 Lines: 17 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.