From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755558Ab2KUS0V (ORCPT ); Wed, 21 Nov 2012 13:26:21 -0500 Received: from terminus.zytor.com ([198.137.202.10]:53299 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755471Ab2KUS0U (ORCPT ); Wed, 21 Nov 2012 13:26:20 -0500 Message-ID: <50AD1CB6.9030707@zytor.com> Date: Wed, 21 Nov 2012 10:25:58 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121029 Thunderbird/16.0.2 MIME-Version: 1.0 To: Sasha Levin CC: tglx@linutronix.de, mingo@redhat.com, x86@kernel.org, linux-kernel@vger.kernel.org, penberg@kernel.org Subject: Re: [PATCH] x86, smpboot: allow manual hotplug of CPUs References: <1353522136-14944-1-git-send-email-sasha.levin@oracle.com> In-Reply-To: <1353522136-14944-1-git-send-email-sasha.levin@oracle.com> X-Enigmail-Version: 1.4.6 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/21/2012 10:22 AM, Sasha Levin wrote: > So far CPU hotplug was ignored for mptable implementations which support it by > having the hotpluggable CPUs marked as disabled during boot. > > The current kernel code detects that behaviour and actually deals with it > properly: > > [ 0.000000] Intel MultiProcessor Specification v1.4 > [ 0.000000] MPTABLE: OEM ID: KVMCPU00 > [ 0.000000] MPTABLE: Product ID: 0.1 > [ 0.000000] MPTABLE: APIC at: 0xFEE00000 > [ 0.000000] Processor #0 (Bootup-CPU) > [ 0.000000] Processor #1 > [ 0.000000] Processor #2 > [ 0.000000] IOAPIC[0]: apic_id 4, version 17, address 0xfec00000, GSI 0-23 > [ 0.000000] Processors: 3 > [ 0.000000] smpboot: Allowing 3 CPUs, 1 hotplug CPUs > > The problem begins when a user might actually want to online such CPU; there > is no interface for him to tell the kernel that the CPU is now present and > can be used. > > Luckily, the kernel provides a generic interface in the form of 'probe' and > 'release' sysfs files which are used on different architectures exactly for > that - to probe and release CPUs. On x86 however this was unimplemented > until now. > > This patch adds code into the x86 implementation of probe and release to allow > adding and removing CPUs. This allows machines that use mptable to hotplug > CPUs: > Reading between the lines, this sounds like would cause a user-visible difference between mptable platforms and ACPI platforms? If so, that is totally unacceptable. If not, the description is confusing. -hpa