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Re: [libvirt] [PATCH] Support VCPU hotplug in QEMU guests



On 02/16/2010 07:12 AM, Daniel P. Berrange wrote:
> QEMU has a monitor command 'set_cpu' which allows a specific
> CPU to be toggled between online& offline state. libvirt CPU
> hotplug does not work in terms of individual indexes CPUs.
> Thus to support this, we iteratively toggle the online state
> when the total number of vCPUs is adjusted via libvirt
> 
> NB, currently untested since QEMU segvs when running this!
> 
> * src/qemu/qemu_driver.c: Toggle online state for CPUs when
>   doing hotplug
> * src/qemu/qemu_monitor.c, src/qemu/qemu_monitor.h,
>   src/qemu/qemu_monitor_json.c, src/qemu/qemu_monitor_json.h,
>   src/qemu/qemu_monitor_text.c, src/qemu/qemu_monitor_text.h: Add
>   monitor API for toggling a CPU's online status via 'set_cpu
> ---
>  src/qemu/qemu_driver.c       |   59 ++++++++++++++++++++++++++++++++++++-----
>  src/qemu/qemu_monitor.c      |   14 ++++++++++
>  src/qemu/qemu_monitor.h      |    2 +
>  src/qemu/qemu_monitor_json.c |   44 +++++++++++++++++++++++++++++++
>  src/qemu/qemu_monitor_json.h |    1 +
>  src/qemu/qemu_monitor_text.c |   38 +++++++++++++++++++++++++++
>  src/qemu/qemu_monitor_text.h |    1 +
>  7 files changed, 151 insertions(+), 8 deletions(-)
> 


Whoops, this made me realize I didn't actually push my changes to
SetVcpus in the qemu driver. I've just done so.

...

>  static int qemudDomainSetVcpus(virDomainPtr dom, unsigned int nvcpus) {
>      struct qemud_driver *driver = dom->conn->privateData;
>      virDomainObjPtr vm;
> @@ -4228,12 +4273,6 @@ static int qemudDomainSetVcpus(virDomainPtr dom, unsigned int nvcpus) {
>      if (qemuDomainObjBeginJob(vm) < 0)
>          goto cleanup;
>  
> -    if (virDomainObjIsActive(vm)) {
> -        qemuReportError(VIR_ERR_OPERATION_INVALID, "%s",
> -                        _("cannot change vcpu count of an active domain"));
> -        goto endjob;
> -    }
> -
>      if (!(type = virDomainVirtTypeToString(vm->def->virtType))) {
>          qemuReportError(VIR_ERR_INTERNAL_ERROR,
>                          _("unknown virt type in domain definition '%d'"),
> @@ -4254,8 +4293,12 @@ static int qemudDomainSetVcpus(virDomainPtr dom, unsigned int nvcpus) {
>          goto endjob;
>      }
>  
> -    vm->def->vcpus = nvcpus;
> -    ret = 0;
> +    if (virDomainObjIsActive(vm)) {
> +        ret = qemudDomainHotplugVcpus(vm, nvcpus);
> +    } else {
> +        vm->def->vcpus = nvcpus;
> +        ret = 0;
> +    }
>  

This portion will need to be rebased. Most important is to drop the
inactive fallback above.

Thanks,
Cole


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