Re: [Qemu-devel] [PATCH v7] docs: add cpu-hotplug.txt

[Dou Liyang]

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