On Mon, Aug 08, 2016 at 10:28:02AM +0800, Dou Liyang wrote: > This document describes how to use cpu hotplug in QEMU. > > Signed-off-by: Dou Liyang <douly.f...@cn.fujitsu.com> > --- > docs/cpu-hotplug.txt | 110 > +++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 110 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..d62638e > --- /dev/null > +++ b/docs/cpu-hotplug.txt > @@ -0,0 +1,110 @@ > +QEMU CPU hotplug > +=================== > + > +This document explains how to use the cpu hotplug feature in QEMU, > +which is present since v2.6.0. > + > +Guest support is required for cpu hotplug to work. > + > +CPU hotplug > +------------------- > + > +In order to be able to hotplug cpu, QEMU has to be told what is the
a cpu > +maximum amount of cpus the guest can grow. This is done at startup /grow/have/ > +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" set the number of CPUs to 'n' [default=1] /set/sets/ > + - "maxcpus" maximum number of total cpus, including offlineCPUs for is the maximum... remove the word 'total' > + hotplug, etc > + - "cores" number of CPU cores on one socket is the number > + - "threads= number of threads on one CPU core is the number > + - "sockets= number of discrete sockets in the system is the number > + > + > +For example, the following command-line: > + > + qemu [...] -smp 3,maxcpus=10,sockets=2,cores=2,threads=2 > + > +Creates a guest with 3 cpus and it support up to 10 cpus. The cpu /it support/supports/ > +topology is sockets (2) * cores (2) * threads (2) and can't greater > +than maxcpus. The topology should exactly provide maxcpus, i.e. this example is wrong because the topology only provides a maximum of 8 cpus, but maxcpus=10. Indeed specifying maxcpus is redundant when a complete topology is given. > When the guest is just booted, the guest will see 3 ^^ it > +cpus. so there are seven cpus can be hotplugged by using any Five cpus may be hotplugged using any ... > +combination of the available sockets,cores and threads topology or sockets, cores, and threads I'm not sure what the "using any combination..." means though. > +using apic-id. by using > + > +cpu hot-plug > +----------------------- > + > +A monitor commands are used to hotplug cpu: /A monitor/Monitor/ /cpu/cpus/ > + > + - "device_add": creates a cpu device and inserts it into the > + specific topology as a device > + > +For example, the following commands add a cpu which id is cpu1 to /commands add/command adds/ > +the guest discussed earlier: a guest: > + > + (qemu) device_add qemu64-x86_64-cpu,id=cpu1,apic-id=3 > + > + - "qemu64-x86_64-cpu" is the cpu modle. /modle/model/ > + - "id" is the unique identifier in the device sets. /sets/set/ > + - "apic-id" is the hotpluged cpu's physical identification. > + > +Another command uses the cpu topology to add the additional cpu in /the cpu topology/cpu topology/ > +the designated position. > + > +For example, the following commands add a cpu in the last position > +of the guest cpu topology discussed earlier. command adds a cpu to position socket=2, core=1, thread=1: > + > + (qemu) device_add qemu64-x86_64-cpu,id=cpu1,socket-id=2,core-id=1, > + thread-id=1 > + > +It's also possible to start a guest with cpu cold-plugged into the with a cpu > +hotpluggable cpu topology. > + > +In the following command-line example, a guest which has 3 cpus is > +created where one of the cpus comes from the "apic-id", and another > +one comes from "socket-id...". After that, the guest has additional > +seven cpus to be hot-plug when needed: > + > + qemu [...] -smp 1,maxcpus=10,sockets=2,cores=2,threads=2 Broken example again; 2*2*2 != 10 > + -device qemu64-x86_64-cpu,id=cpu1,apic-id=1 > + -device qemu64-x86_64-cpu,socket-id=2,core-id=1,thread-id=0 > + > +cpu hot-unplug > +------------------------ > + > +In order to be able to hot unplug cpu device, QEMU has two ways > +to remove cpu device. a cpu device /ways to remove cpu device/methods of removal;/ > + 1. Using the ids which were assigned when you hot plugged cpus. s/you hot plugged/hotplugging/ > + 2. Using qom_path where the cpu is located in the guest. Using the qom_path of the cpu. > + > +A monitor commands are used to hot unplug cpus: /Monitor commands/ > + > + - "device_del": deletes a cpu device > + > +For example, assuming that the cpu device with id "cpu1" exists, > +the following commands tries to remove it. /commands/command/ /./:/ > + > + (qemu) device_del cpu1 > + > +If you don't set the ids when you hot plugged cpus. > + > +First, you may need to obtain the cpu's qom_path. The following If the IDs are not set when hotplugging, then the cpu's qom_path needs to be obtained. > +commands list all hotplugable-cpus, you can get the qom_path > +through the cpu topology. /commands list/command lists/ > + > + (qemu) info hotpluggable-cpus > + > +Then you can remove it by the qom_path. Drop this sentence. > + > +For example, assuming that the cpu device with qom_path "/machine > +/unattached/device[0]" exists, the following commands tries to /commands/command/ > +remove it. > + > + (qemu) device_del /machine/unattached/device[0] > -- > 2.5.5 > > > > Thanks, drew