Hello, I'm looking to implement cpu hotplug,
and I have a question about cpu flags currently I have something like -cpu qemu64,+lahf_lm,+sep,+kvm_pv_unhalt,+kvm_pv_eoi,enforce -smp 4,sockets=2,cores=2,maxcpus=4 Does I need to define flags like: -smp 2,sockets=2,cores=2,maxcpus=4 -device qemu64-x86_64-cpu,+lahf_lm,+sep,+kvm_pv_unhalt,+kvm_pv_eoi,enforce,id=cpu1,socket-id=1,core-id=1,thread-id=0 ... ? Another question, is -smp mandatory ? (if I want coldplug all cpus) -smp sockets=2,cores=2,maxcpus=4 -device qemu64-x86_64-cpu,id=cpu1,socket-id=1,core-id=1,thread-id=0 -device qemu64-x86_64-cpu,id=cpu1,socket-id=1,core-id=2,thread-id=0 -device qemu64-x86_64-cpu,id=cpu3,socket-id=2,core-id=1,thread-id=0 -device qemu64-x86_64-cpu,id=cpu4,socket-id=2,core-id=2,thread-id=0 or does I need minimum 1 non unplugable cpu -smp 1,sockets=2,cores=2,maxcpus=4 -device qemu64-x86_64-cpu,id=cpu1,socket-id=1,core-id=2,thread-id=0 -device qemu64-x86_64-cpu,id=cpu3,socket-id=2,core-id=1,thread-id=0 -device qemu64-x86_64-cpu,id=cpu4,socket-id=2,core-id=2,thread-id=0 Regards, Alexandre ----- Mail original ----- De: "Dou Liyang" <douly.f...@cn.fujitsu.com> À: "qemu-devel" <qemu-devel@nongnu.org> Cc: "Dou Liyang" <douly.f...@cn.fujitsu.com>, drjo...@redhat.com, "ehabkost" <ehabk...@redhat.com>, "Markus Armbruster" <arm...@redhat.com>, bhar...@linux.vnet.ibm.com, "Fam Zheng" <f...@redhat.com>, "Igor Mammedov" <imamm...@redhat.com>, da...@gibson.dropbear.id.au Envoyé: Jeudi 18 Août 2016 03:50:50 Objet: [Qemu-devel] [PATCH v7] docs: add cpu-hotplug.txt This document describes how to use cpu hotplug in QEMU. Signed-off-by: Dou Liyang <douly.f...@cn.fujitsu.com> Reviewed-by: Andrew Jones <drjo...@redhat.com> --- 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 + -- 2.5.5
