Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752730Ab0ALUhM (ORCPT ); Tue, 12 Jan 2010 15:37:12 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751511Ab0ALUhL (ORCPT ); Tue, 12 Jan 2010 15:37:11 -0500 Received: from nlpi157.sbcis.sbc.com ([207.115.36.171]:47533 "EHLO nlpi157.prodigy.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751444Ab0ALUhK (ORCPT ); Tue, 12 Jan 2010 15:37:10 -0500 Date: Tue, 12 Jan 2010 14:31:53 -0600 (CST) From: Christoph Lameter X-X-Sender: cl@router.home To: Yinghai Lu cc: Suresh Siddha , Linus Torvalds , "ananth@in.ibm.com" , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 1/5] use nr_cpus= to set nr_cpu_ids early In-Reply-To: <86802c441001121157y5cdc1a91g2a66d8591d6fd579@mail.gmail.com> Message-ID: References: <1263298146-25597-1-git-send-email-yinghai@kernel.org> <86802c441001121157y5cdc1a91g2a66d8591d6fd579@mail.gmail.com> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1159 Lines: 26 On Tue, 12 Jan 2010, Yinghai Lu wrote: > > Why do we need this twice? > > maxcpus only change setup_max_cpus., and if you are using maxcpus=1, > and you have 8 cpus installed, you can put other > cpus back online via /sys/interface. Hmmm.. Strange semantics since maxcpus=0 disables smp completely. No cpu can be activated later. Similar to nr_cpus ? > nr_cpus= is hard limit nr_cpu_ids, so if you have 16 cpus installed, > nr_cpus=8 will make your nr_cpu_ids=8, and you can not put back > other 8 back. and apic mode could stay with logical flat. > this is used to simulate some debug case. for example you have kernel > support physflat, and flat, with CONFIG_NR_CPUS=255. to run that on > system that only have 8 cpus, you will have apic mode in logical flat. > but if you have run the kernel on system with 32 cpus installed, it > will switch to physflat even you have maxcpus=8 appedded. Ok makes sense. -- 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/