From patchwork Thu Aug 18 01:50:50 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dou Liyang X-Patchwork-Id: 660306 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 3sF8HK1jY9z9t1G for ; Thu, 18 Aug 2016 11:52:28 +1000 (AEST) Received: from localhost ([::1]:50279 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1baCVL-000105-4B for incoming@patchwork.ozlabs.org; Wed, 17 Aug 2016 21:52:23 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54413) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1baCUc-0000iR-1E for qemu-devel@nongnu.org; Wed, 17 Aug 2016 21:51:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1baCUX-0006Y1-IU for qemu-devel@nongnu.org; Wed, 17 Aug 2016 21:51:36 -0400 Received: from [59.151.112.132] (port=43896 helo=heian.cn.fujitsu.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1baCUW-0006XQ-Ja for qemu-devel@nongnu.org; Wed, 17 Aug 2016 21:51:33 -0400 X-IronPort-AV: E=Sophos;i="5.22,518,1449504000"; d="scan'208";a="10026752" Received: from unknown (HELO cn.fujitsu.com) ([10.167.33.5]) by heian.cn.fujitsu.com with ESMTP; 18 Aug 2016 09:51:30 +0800 Received: from G08CNEXCHPEKD02.g08.fujitsu.local (unknown [10.167.33.83]) by cn.fujitsu.com (Postfix) with ESMTP id E0E7B42BC504; Thu, 18 Aug 2016 09:51:28 +0800 (CST) Received: from localhost.localdomain (10.167.226.129) by G08CNEXCHPEKD02.g08.fujitsu.local (10.167.33.89) with Microsoft SMTP Server (TLS) id 14.3.279.2; Thu, 18 Aug 2016 09:51:28 +0800 From: Dou Liyang To: Date: Thu, 18 Aug 2016 09:50:50 +0800 Message-ID: <1471485050-26747-1-git-send-email-douly.fnst@cn.fujitsu.com> X-Mailer: git-send-email 2.5.5 MIME-Version: 1.0 X-Originating-IP: [10.167.226.129] X-yoursite-MailScanner-ID: E0E7B42BC504.A2814 X-yoursite-MailScanner: Found to be clean X-yoursite-MailScanner-From: douly.fnst@cn.fujitsu.com X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 59.151.112.132 Subject: [Qemu-devel] [PATCH v7] docs: add cpu-hotplug.txt X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Dou Liyang , drjones@redhat.com, ehabkost@redhat.com, armbru@redhat.com, bharata@linux.vnet.ibm.com, famz@redhat.com, imammedo@redhat.com, david@gibson.dropbear.id.au Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" This document describes how to use cpu hotplug in QEMU. Signed-off-by: Dou Liyang Reviewed-by: Andrew Jones --- Change log v6 -> v7 From Bharata's advice 1. add "qom_path" property explanation for "info hotpluggable-cpus" command From drew's advice 1. Fix some spelling mistake Change log v5 -> v6 From drew's advice 1. Fix some spelling and grammar mistakes Change log v4 -> v5 1. add an example for sPAPR From Bharata's advice 1. Fix the examples Change log v3 -> v4 From David's advice 1. add spapr examples 2. Fix some comment From drew's advice 1. Fix some syntax Change log v2 -> v3: From drew's advice: 1. modify the examples. 2. Fix some syntax. Change log v1 -> v2: From Fam's advice: 1. Fix some comment. Change log v1: From Igor's advice: 1. Remove any mentioning of apic-id from the document. 2. Remove the "device_del qom_path" from the CPU hot-unplug. 3. Fix some comment. docs/cpu-hotplug.txt | 156 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 156 insertions(+) create mode 100644 docs/cpu-hotplug.txt diff --git a/docs/cpu-hotplug.txt b/docs/cpu-hotplug.txt new file mode 100644 index 0000000..3667641 --- /dev/null +++ b/docs/cpu-hotplug.txt @@ -0,0 +1,156 @@ +QEMU CPU hotplug +================ + +This document explains how to use the CPU hotplug feature in QEMU, +which regards the CPU as a device, using -device/device_add and +device_del. + +QEMU support was merged for 2.7. + +Guest support is required for CPU hotplug to work. + +CPU hot-plug +------------ + +In order to be able to hotplug CPUs, QEMU has to be told the maximum +number of CPUs which the guest can have. This is done at startup time +by means of the -smp command-line option, which has the following +format: + + -smp [cpus=]n[,maxcpus=cpus][,cores=cores][,threads=threads] + [,sockets=sockets] + +where, + + - "cpus" sets the number of CPUs to 'n' [default=1]. + - "maxcpus" sets the maximum number of CPUs, including offline VCPUs + for hotplug. + - "sockets" sets the number of discrete sockets in the system. + - "cores" sets the number of CPU cores on one socket. + - "threads" sets the number of threads on one CPU core. + +For example, the following command-line: + + qemu [...] -smp 4,maxcpus=8,sockets=2,cores=2,threads=2 + +creates a guest with 4 VCPUs and supports up to 8 VCPUs. The CPU topology +is sockets (2) * cores (2) * threads (2) and should compute a number of +slots exactly equal to maxcpus. A computed number of slots greater than +maxcpus will result in error. When the guest finishes loading, the guest +will see 4 VCPUs. More of this below. + +Query available CPU objects +--------------------------- + +To add a VCPU, it must be identified by socket-id, core-id, and/or +thread-id parameters. + +Before adding the VCPU, we should know the topology parameters, so +that we can find the available location (socket,core,thread) for a +new VCPU. + +Use the HMP command "info hotpluggable-cpus" to obtain them, for example: + + (qemu) info hotpluggable-cpus + +lists all CPUs including the present and possible hot-pluggable CPUs. +Such as this: + + ... + type: "qemu64-x86_64-cpu" + vcpus_count: "1" + CPUInstance Properties: + socket-id: "1" + core-id: "0" + thread-id: "0" + type: "qemu64-x86_64-cpu" + vcpus_count: "1" + qom_path: "/machine/unattached/device[4]" + CPUInstance Properties: + socket-id: "0" + core-id: "1" + thread-id: "1" + ... + +or + + ... + type: "POWER7_v2.3-spapr-cpu-core" + vcpus_count: "1" + CPUInstance Properties: + core-id: "2" + type: "POWER7_v2.3-spapr-cpu-core" + vcpus_count: "1" + qom_path: "/machine/unattached/device[2]" + CPUInstance Properties: + core-id: "1" + ... + +The property called "qom_path" indicates that the listed CPU is already +present or plugged-in. + +Different platforms may have different "CPUInstance Properties", which +will be used in hot-plugging below. + +Hotplug CPUs +------------ + +A monitor command may be used to hotplug CPUs: + + - "device_add": creates a CPU device and inserts it into the + specific location. + +For example, the following command adds a VCPU, which has the id cpu1, +to a specific location in the topology (socket=1,core=0,thread=0): + + (qemu) device_add qemu64-x86_64-cpu,id=cpu1,socket-id=1,core-id=0,thread-id=0 + +where, + + - "qemu64-x86_64-cpu" is the CPU model. + - "id" is the unique identifier in the device set. + - "socket-id/core-id/thread-id" represent the designated location, + which is obtained from the above possible list of CPUs. + +It's also possible to start a guest with a CPU cold-plugged into a +specific location (socket,core,thread). + +In the following command line example, a guest which has 4 VCPUs is +created: + + qemu [...] -smp 2,maxcpus=8,sockets=2,cores=2,threads=2 \ + -device qemu64-x86_64-cpu,id=cpu1,socket-id=1,\ + core-id=1,thread-id=0 \ + -device qemu64-x86_64-cpu,id=cpu2,socket-id=1,\ + core-id=1,thread-id=1 \ + +Two VCPUs are cold-plugged by the "-device" parameter, which are in +the same socket and core, but with different thread-ids. After that, +the guest has an additional four VCPUs available for hot-plug when +needed. + +The above example is for an x86 machine type. The topology parameters +and resulting number of online VCPUs may not be suitable for other +platforms. The "CPUInstance Properties" output described above lists +the valid topology parameters. + +For example, the following command adds a VCPU in an sPAPR hardware +system: + + (qemu) device_add POWER7_v2.3-spapr-cpu-core,id=cpu1,core-id=2 + +CPU hot-unplug +-------------- + +In order to be able to hot unplug a CPU device, QEMU removes the +device by using the id which was assigned when hotplugging it. + +A monitor command may be used to hot unplug CPUs: + + - "device_del": deletes a CPU device + +For example, assuming that the CPU device with id "cpu1" exists, +then the following command tries to remove it. + + (qemu) device_del cpu1 +