Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759429AbYHZUBa (ORCPT ); Tue, 26 Aug 2008 16:01:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758985AbYHZUBG (ORCPT ); Tue, 26 Aug 2008 16:01:06 -0400 Received: from relay2.sgi.com ([192.48.171.30]:42485 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1758943AbYHZUBF (ORCPT ); Tue, 26 Aug 2008 16:01:05 -0400 Message-ID: <48B460FE.2020100@sgi.com> Date: Tue, 26 Aug 2008 13:01:02 -0700 From: Mike Travis User-Agent: Thunderbird 2.0.0.6 (X11/20070801) MIME-Version: 1.0 To: Dave Jones , Linus Torvalds , Mike Travis , "Alan D. Brunelle" , Ingo Molnar , Thomas Gleixner , "Rafael J. Wysocki" , Linux Kernel Mailing List , Kernel Testers List , Andrew Morton , Arjan van de Ven , Rusty Russell , "Siddha, Suresh B" , "Luck, Tony" , Jack Steiner , Christoph Lameter Subject: Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c - bisected References: <48B29F7B.6080405@hp.com> <48B2A421.7080705@hp.com> <48B313E0.1000501@hp.com> <48B452F3.9040304@sgi.com> <20080826192848.GA20653@redhat.com> In-Reply-To: <20080826192848.GA20653@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1368 Lines: 30 Dave Jones wrote: ... > > But yes, for this to be even remotely feasible, there has to be a negligable > performance cost associated with it, which right now, we clearly don't have. > Given that the number of people running 4096 CPU boxes even in a few years time > will still be tiny, punishing the common case is obviously absurd. > > Dave > I did do some fairly extensive benchmarking between configs of NR_CPUS = 128 and 4096 and most performance hits were in the neighborhood of < 5% on systems with 8 cpus and 4GB of memory (our most common test system). [But changing cpumask_t's to be pointers instead of values will likely increase this.] I've tried to be very sensitive to this issue with all my previous changes, so convincing the distros to set NR_CPUS=4096 would be as painless for them as possible. ;-) Btw, huge count cpu systems I don't think are that far away. I believe the nextgen Larabbee chips will be geared towards HPC applications [instead of just GFX apps], and putting 4 of these chips on a motherboard would add up to 512 cpu threads (1024 if they support hyperthreading.) Thanks, Mike -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/