On Mon, Aug 15, 2016 at 01:49:48PM +0800, Dou Liyang wrote: > This document describes how to use cpu hotplug in QEMU. > > Signed-off-by: Dou Liyang <douly.f...@cn.fujitsu.com> > --- > 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 | 127 > +++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 127 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..892505f > --- /dev/null > +++ b/docs/cpu-hotplug.txt > @@ -0,0 +1,127 @@ > +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, etc.
Not sure what the 'etc.' is for. Drop it if there's nothing else, or state explicitly what the other reason(s) are. > + - "cores" sets the number of CPU cores on one socket. > + - "threads" sets the number of threads on one CPU core. > + - "sockets" sets the number of discrete sockets in the system. On > + sPAPR, sockets have no real meaning, And it has no real effect. Please correct this list to be in either ascending or descending hierarchical order; i.e. sockets,cores,threads or threads,cores,sockets I think the sPAPR note should be in () > + > +For example, the following command-line: > + > + qemu [...] -smp 3,maxcpus=8,sockets=2,cores=2,threads=2 > + > +Creates a guest with 3 VCPUs and it supports up to 8 VCPUs. The lowercase c on Creates, as we're continuing the above sentence. /it supports/supports/ > +CPU topology is sockets (2) * cores (2) * threads (2) and can't be > +greater than maxcpus. When the guest is booted, the guest will see The CPU topology, sockets (2) * cores (2) * threads (2), allows for 8 CPU slots, which exactly matches maxcpus. /booted/boot/ > +3 VCPUs. More on this below. > + > +Query possible available CPU objects /possible// > +------------------------------------ > + > +The VCPUs should be hotplugged by socket/core/thread-id parameters , after parameters > +describing the available CPU objects. > + > +Before adding the VCPUs, we should know those topology parameters, > +so that we can find the available location (socket,core,thread) for > +a new VCPU. > + > +There are two ways to obtain them: > + > +1. Using the properties advertised by QEMU via the QMP command > +"query-hotpluggable-cpus". For enumerated lists please space additional lines under the start of the text, e.g. 1. This line is too long and therefore needs to be continued on the next line. > +2. Using the corresponding HMP command "info hotpluggable-cpus". > + > +For example, a monitor command can be used to list the possible CPU > +objects: > + > + (qemu) info hotpluggable-cpus > + > +Select the hotpluggable CPUs including "CPUInstance Properties" for > +hotpluging. Such as this: hotplugging > + > + ... > + type: "qemu64-x86_64-cpu" > + vcpus_count: "1" > + CPUInstance Properties: > + socket-id: "0" > + core-id: "1" > + thread-id: "0" > + ... > + > +Hotplug CPUs > +------------ > + > +A monitor command can be used to hotplug CPUs: > + > + - "device_add": creates a VCPU device and inserts it into the > + specific place as a device > + > +For example, the following command adds a VCPU which has the id cpu1 > +in the specific position of the guest's CPU sockets which was discussed > +earlier by using the socket/core/thread-id: No need to refer to the previous example. It makes no difference in this example. I suggest just For example, the following command adds a VCPU, which has the id cpu1, to a specific location in the topology (socket=0,core=1,thread=1): > + > + (qemu) device_add > qemu64-x86_64-cpu,id=cpu1,socket-id=0,core-id=1,thread-id=1 > + > +Where, > + > + - "qemu64-x86_64-cpu" is the CPU model. > + - "id" is the unique identifier in the device set. It is required. > + - "socket-id/core-id/thread-id" represent the designated position /position/location,/ > + which is obtained form 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 3 VCPUs is > +created: > + > + qemu [...] -smp 1,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 "-device" parameter, which are in the > +same socket and core but with different thread-ids. After that, the , after core > +guest has an additional five VCPUs to be hot-plugged when needed. > + > +CPU hot-unplug > +-------------- > + > +In order to be able to hot unplug a CPU device, QEMU removes CPU > +devices by using the ids which were assigned when hotplugging the > +CPU device. > + > +A monitor command can be used to hot unplug CPUs: > + > + - "device_del": deletes a CPU device > + > +For example, assuming that the CPU device with id "cpu1" exists and has > +been offline, the following command tries to remove it. For example, assuming that a CPU device with an id "cpu1" exists, and has been offlined, then the following command tries to remove it: > + > + (qemu) device_del cpu1 > + > -- > 2.5.5 Thanks, drew
