Re: [Qemu-devel] multiprocessor on kvm

[Xin Tong]

so qemu exposes multiple processors to the guest os by having multiple
vCPUs. and it realizes the multiple vCPUs by either using RR on a
single host cpu (qemu ) or using multiple host cpus (kvm).

Thanks

Xin


2011/11/8 Stefan Hajnoczi <address@hidden>:
> On Tue, Nov 8, 2011 at 12:10 PM, 陳韋任 <address@hidden> wrote:
>> On Tue, Nov 08, 2011 at 08:04:44PM +0800, 陳韋任 wrote:
>>> > I am wondering that when one uses qemu with kvm. How many cores are
>>> > exposed and available to the guest os ( assuming the host has 4 cores
>>> > ). is this configurable ?
>>>
>>>   QEMU provides "-smp" option, but those virtual cpus are scheduled in
>>> round-robin fashion. In other words, it's not real parallelism. I don't
>>> know if there is any difference with kvm enabled.
>>
>>  IIRC, kvm uses QEMU for device emulation only. Those virtual cpus are
>> ran on physical cpus simultaneously.
>
> Right, qemu -enable-kvm will run a thread for each vCPU.  So you get
> true SMP parallelism.
>
> QEMU without KVM mode, on the other hand, does round-robin scheduling
> of vCPUs and does not take advantage of multiprocessor hosts.
>
> Stefan
>