Re: [Qemu-devel] [PATCH 4/5] pc: add cpu hotplug handler to PC_MACHINE

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 12 Sep 2014 11:02:09 +0800
Gu Zheng <guz.fnst@cn.fujitsu.com> wrote:

> Hi Igor,
> On 09/10/2014 09:55 PM, Igor Mammedov wrote:
> 
> > On Wed,  3 Sep 2014 17:06:16 +0800
> > Gu Zheng <guz.fnst@cn.fujitsu.com> wrote:
> > 
> >> Add cpu hotplug handler to PC_MACHINE, which will perform the acpi
> >> cpu hotplug callback via hotplug_handler API.
> >>
> >> Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
> >> ---
> >>  hw/i386/pc.c |   26 +++++++++++++++++++++++++-
> >>  qom/cpu.c    |    1 -
> >>  2 files changed, 25 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> >> index 8fa8d2f..c2956f9 100644
> >> --- a/hw/i386/pc.c
> >> +++ b/hw/i386/pc.c
> >> @@ -1607,11 +1607,34 @@ out:
> >>      error_propagate(errp, local_err);
> >>  }
> >>  
> >> +static void pc_cpu_plug(HotplugHandler *hotplug_dev,
> >> +                         DeviceState *dev, Error **errp)
> >> +{
> >> +    HotplugHandlerClass *hhc;
> >> +    Error *local_err = NULL;
> >> +    PCMachineState *pcms = PC_MACHINE(hotplug_dev);
> >> +
> >> +    if (dev->hotplugged) {
> > for startup CPUs we set gpe_cpu status bits in AcpiCpuHotplug_init()
> > and for hotpluged in AcpiCpuHotplug_add() which is duplicating
> > essentially the same code.
> > 
> > Could you drop above check and make AcpiCpuHotplug_init() take care
> > about startup CPUs as well, keeping bit setting in one place.
> 
> Yeah, with the above change, code will be more neat, but I think it is not
> a serious problem.:)
> And pcms->acpi_dev is set when PC hardware initialisation (e.g. pc_init1),
> for start up cpus, the plug handler is not valid, so the check is needed
> here to avoid trigger error by start cpu.

then check for !pcms->acpi_dev and exit if it not set (i.e. as pc_dimm_plug() does)
since there isn't acpi hardware to update for startup CPUs either.

may be something along this lines:

if (!pcms->acpi_dev) {
  if (dev->hotplugged) error_setg(&local_err, "CPU hotplug is not supported without ACPI");
  goto out;
}

> 
> > 
> >> +        if (!pcms->acpi_dev) {
> >> +            error_setg(&local_err,
> >> +                   "cpu hotplug is not enabled: missing acpi device");
> >> +            goto out;
> >> +        }
> >> +
> >> +        hhc = HOTPLUG_HANDLER_GET_CLASS(pcms->acpi_dev);
> >> +        hhc->plug(HOTPLUG_HANDLER(pcms->acpi_dev), dev, &local_err);
> >> +out:
> >> +        error_propagate(errp, local_err);
> >> +    }
> >> +}
> >> +
> >>  static void pc_machine_device_plug_cb(HotplugHandler *hotplug_dev,
> >>                                        DeviceState *dev, Error **errp)
> >>  {
> >>      if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
> >>          pc_dimm_plug(hotplug_dev, dev, errp);
> >> +    } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
> >> +        pc_cpu_plug(hotplug_dev, dev, errp);
> >>      }
> >>  }
> >>  
> >> @@ -1620,7 +1643,8 @@ static HotplugHandler *pc_get_hotpug_handler(MachineState *machine,
> >>  {
> >>      PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(machine);
> >>  
> >> -    if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
> >> +    if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)
> >> +        || object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
> >>          return HOTPLUG_HANDLER(machine);
> >>      }
> >>  
> >> diff --git a/qom/cpu.c b/qom/cpu.c
> >> index b32dd0a..af8e83f 100644
> >> --- a/qom/cpu.c
> >> +++ b/qom/cpu.c
> >> @@ -304,7 +304,6 @@ static void cpu_common_realizefn(DeviceState *dev, Error **errp)
> >>      if (dev->hotplugged) {
> >>          cpu_synchronize_post_init(cpu);
> >>          notifier_list_notify(&cpu_added_notifiers, dev);
> >> -        cpu_resume(cpu);
> >>      }
> >>  }
> >>  
> > 
> > I don't see what sets PCMachine as hotplug_handler for CPU,
> > maybe series is missing a patch?
> 
> Previous memory hotplug has built the frame work, here just adding the case
> to handle CPU.
You still need to set hotplug handler for CPU device or ICCBus
grep for qbus_set_hotplug_handler()

> 
>  static void pc_machine_device_plug_cb(HotplugHandler *hotplug_dev,
>                                        DeviceState *dev, Error **errp)
>  {
>      if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
>          pc_dimm_plug(hotplug_dev, dev, errp);
> +    } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
> +        pc_cpu_plug(hotplug_dev, dev, errp);
>      }
> 
> Thanks,
> Gu
> 
> > 
> > .
> > 
> 
>