Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422925AbWBIRhg (ORCPT ); Thu, 9 Feb 2006 12:37:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1422922AbWBIRhf (ORCPT ); Thu, 9 Feb 2006 12:37:35 -0500 Received: from colin.muc.de ([193.149.48.1]:39179 "EHLO mail.muc.de") by vger.kernel.org with ESMTP id S1422926AbWBIRhe (ORCPT ); Thu, 9 Feb 2006 12:37:34 -0500 Date: 9 Feb 2006 18:37:26 +0100 Date: Thu, 9 Feb 2006 18:37:26 +0100 From: Andi Kleen To: Heiko Carstens Cc: Nathan Lynch , Andrew Morton , Eric Dumazet , riel@redhat.com, linux-kernel@vger.kernel.org, torvalds@osdl.org, mingo@elte.hu, 76306.1226@compuserve.com, wli@holomorphy.com, Paul Jackson Subject: Re: [PATCH] percpu data: only iterate over possible CPUs Message-ID: <20060209173726.GA39278@muc.de> References: <200602051959.k15JxoHK001630@hera.kernel.org> <20060208190512.5ebcdfbe.akpm@osdl.org> <20060208190839.63c57a96.akpm@osdl.org> <43EAC6BE.2060807@cosmosbay.com> <20060208204502.12513ae5.akpm@osdl.org> <20060209160808.GL18730@localhost.localdomain> <20060209161331.GE20554@osiris.boeblingen.de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060209161331.GE20554@osiris.boeblingen.de.ibm.com> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1248 Lines: 26 On Thu, Feb 09, 2006 at 05:13:31PM +0100, Heiko Carstens wrote: > > > Presumably not all architectures are doing that. > > powerpc/ppc64, for instance, determines the number of possible cpus > > from information exported by firmware (and I'm mystified as to why > > other platforms don't do this). So it's typical to have a kernel an a > > pSeries partition with NR_CPUS=128, but cpu_possible_map = 0xff. > > Simply because there is no such interface on s390. The only thing we know > for sure is that if we are running under z/VM the user is free to > configure up to 63 additional virtual cpus on the fly... x86-64 had the same problem, but we now require that you boot with additional_cpus=... for how many you want. Default is 0 (used to be half available CPUs but that lead to confusion) Also the firmware has a way now to give this information automatically. You can of course make it default to 64, but it will cost you several MB of memory in usually unused copies of per cpu data. -Andi - 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/