| Message ID | 218747645.338872.1471856165532.JavaMail.zimbra@oxygem.tv (mailing list archive) |
|---|---|
| State | New, archived |
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Hi Alexandre, At 08/22/2016 04:56 PM, Alexandre DERUMIER wrote: > 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 I think we don't need to do that. In my option, just like this: -device qemu64-x86_64-cpu,id=cpu1,socket-id=1,.. Because QEMU sets the "-cpu" options in MachineState: current_machine->cpu_model = cpu_model; when you add a CPU, QEMU can get the flag from the MachineState. > ... > > ? > > > Another question, > is -smp mandatory ? (if I want coldplug all cpus) it's not mandatory. such as this: ./x86_64-softmmu/qemu-system-x86_64 -m 1G /image/fedora.img -enable-kvm -monitor stdio (qemu) info cpus * CPU #0: pc=0xffffffff81060586 (halted) thread_id=4032 the default number of CPUs is 1. > > -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 > I think that is better, and the socket-id/core-id/thread-id starts at index 0 I am new to the community. Please don't mind, and take with a grain of salt. Thanks, Dou
On Tue, Aug 23, 2016 at 01:17:01PM +0800, Dou Liyang wrote: > Hi Alexandre, > > At 08/22/2016 04:56 PM, Alexandre DERUMIER wrote: > > 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 > > I think we don't need to do that. > In my option, just like this: > > -device qemu64-x86_64-cpu,id=cpu1,socket-id=1,.. > > Because QEMU sets the "-cpu" options in MachineState: > > current_machine->cpu_model = cpu_model; > > when you add a CPU, QEMU can get the flag from the MachineState. You don't need to repeat the flags, but that's not because of MachineState::cpu_model, but because of the semantics of -smp: The option: -smp MODEL,+FOO,+BAR is internally translated to: -global MODEL.FOO=on -global MODEL.BAR=on in addition to setting the CPU model for creating initial CPUs to MODEL. > > > ... > > > > ? > > > > > > Another question, > > is -smp mandatory ? (if I want coldplug all cpus) > > it's not mandatory. such as this: > > ./x86_64-softmmu/qemu-system-x86_64 -m 1G /image/fedora.img > -enable-kvm -monitor stdio > > (qemu) info cpus > * CPU #0: pc=0xffffffff81060586 (halted) thread_id=4032 > > the default number of CPUs is 1. > > > > > -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 As mentioned above, the default number of CPUs is 1, so "-smp sockets=2" is the same as "-smp 1,sockets=2". I assume you mean something like "-smp 0", but that doesn't work today. I would like to eventually allow all CPUs to be created using -device, but that's not possible yet. > > > > -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 > > > > I think that is better, and the socket-id/core-id/thread-id starts at > index 0 > > I am new to the community. Please don't mind, and take with a grain of > salt. > > Thanks, > Dou > >
Hi, Eduardo At 09/07/2016 04:05 AM, Eduardo Habkost wrote: > On Tue, Aug 23, 2016 at 01:17:01PM +0800, Dou Liyang wrote: >> Hi Alexandre, >> >> At 08/22/2016 04:56 PM, Alexandre DERUMIER wrote: >>> 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 >> >> I think we don't need to do that. >> In my option, just like this: >> >> -device qemu64-x86_64-cpu,id=cpu1,socket-id=1,.. >> >> Because QEMU sets the "-cpu" options in MachineState: >> >> current_machine->cpu_model = cpu_model; >> >> when you add a CPU, QEMU can get the flag from the MachineState. > > You don't need to repeat the flags, but that's not because of > MachineState::cpu_model, but because of the semantics of -smp: Sorry for the reply. > > The option: > -smp MODEL,+FOO,+BAR I guess you may mean "-cpu", not "-smp" > is internally translated to: > -global MODEL.FOO=on > -global MODEL.BAR=on > in addition to setting the CPU model for creating initial CPUs to > MODEL. > I see. >> >>> ... >>> >>> ? >>> >>> >>> Another question, >>> is -smp mandatory ? (if I want coldplug all cpus) >> >> it's not mandatory. such as this: >> >> ./x86_64-softmmu/qemu-system-x86_64 -m 1G /image/fedora.img >> -enable-kvm -monitor stdio >> >> (qemu) info cpus >> * CPU #0: pc=0xffffffff81060586 (halted) thread_id=4032 >> >> the default number of CPUs is 1. >> >>> >>> -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 > > As mentioned above, the default number of CPUs is 1, so "-smp > sockets=2" is the same as "-smp 1,sockets=2". > > I assume you mean something like "-smp 0", but that doesn't work > today. I would like to eventually allow all CPUs to be created > using -device, but that's not possible yet. I am interested in what is the benefit, if we can create all CPUs using -device. :) Thanks, Dou > >>> >>> -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 >>> >> >> I think that is better, and the socket-id/core-id/thread-id starts at >> index 0 >> >> I am new to the community. Please don't mind, and take with a grain of >> salt. >> >> Thanks, >> Dou >> >> >
On Wed, Sep 07, 2016 at 09:52:59AM +0800, Dou Liyang wrote: [...] > > > > The option: > > -smp MODEL,+FOO,+BAR > > I guess you may mean "-cpu", not "-smp" Oops, yes. Thanks. :) > > > is internally translated to: > > -global MODEL.FOO=on > > -global MODEL.BAR=on > > in addition to setting the CPU model for creating initial CPUs to > > MODEL. > > > > I see. > [...] > > > > > > > > -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 > > > > As mentioned above, the default number of CPUs is 1, so "-smp > > sockets=2" is the same as "-smp 1,sockets=2". > > > > I assume you mean something like "-smp 0", but that doesn't work > > today. I would like to eventually allow all CPUs to be created > > using -device, but that's not possible yet. > > I am interested in what is the benefit, if we can create all CPUs using > -device. :) Do you mean the benefit of not allowing "-smp 0", or the benefit of using -device? The benefit of not allowing "-smp 0" is none, except that we probably have existing code that would break if we allow that, and that code needs to be fixed first. About -device: the benefit is having an uniform interface to create every kind of device, and using the same interface and options for hotplugged CPUs and non-hotplug CPUs. (But one problem with -device today is that management software needs to know what are the valid socket/core/thread arguments for the machine but can't run a 'query-hotpluggable-cpus' command before launching QEMU [unless it launches QEMU twice]).
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 +