Re: [Qemu-devel] [PATCH v5 09/10] spapr: CPU hot unplug support

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Nov 20, 2015 at 06:24:38PM +0530, Bharata B Rao wrote:
> Support hot removal of CPU for sPAPR guests by sending the hot unplug
> notification to the guest via EPOW interrupt. Release the vCPU object
> after CPU hot unplug so that vCPU fd can be parked and reused.
> 
> Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> ---
>  hw/ppc/spapr.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 71 insertions(+)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 4434d45..6dca553 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -2401,11 +2401,82 @@ static void spapr_machine_device_plug(HotplugHandler *hotplug_dev,
>      }
>  }
>  
> +static void spapr_cpu_destroy(PowerPCCPU *cpu)
> +{
> +    sPAPRMachineState *spapr = SPAPR_MACHINE(qdev_get_machine());
> +
> +    xics_cpu_destroy(spapr->icp, cpu);
> +    qemu_unregister_reset(spapr_cpu_reset, cpu);
> +}
> +
> +static void spapr_cpu_release(DeviceState *dev, void *opaque)

I'd prefer to see this called "core_release" since "cpu" doesn't make
it clear that it's acting on a whole core.

> +{
> +    CPUState *cs;
> +    int i;
> +    int id = ppc_get_vcpu_dt_id(POWERPC_CPU(CPU(dev)));
> +
> +    for (i = id; i < id + smp_threads; i++) {
> +        CPU_FOREACH(cs) {
> +            PowerPCCPU *cpu = POWERPC_CPU(cs);
> +
> +            if (i == ppc_get_vcpu_dt_id(cpu)) {
> +                spapr_cpu_destroy(cpu);
> +                cpu_remove(cs);
> +            }
> +        }
> +    }
> +}
> +
> +static int spapr_cpu_unplug(HotplugHandler *hotplug_dev, DeviceState *dev,
> +                             Error **errp)
> +{
> +    CPUState *cs = CPU(dev);
> +    PowerPCCPU *cpu = POWERPC_CPU(cs);
> +    int id = ppc_get_vcpu_dt_id(cpu);
> +    int smt = kvmppc_smt_threads();
> +    sPAPRDRConnector *drc =
> +        spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_CPU, id);
> +    sPAPRDRConnectorClass *drck;
> +    Error *local_err = NULL;
> +
> +    /*
> +     * SMT threads return from here, only main thread (core) will
> +     * continue and signal hot unplug event to the guest.
> +     */
> +    if ((id % smt) != 0) {
> +        return 0;
> +    }
> +    g_assert(drc);
> +
> +    drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
> +    drck->detach(drc, dev, spapr_cpu_release, NULL, &local_err);
> +    if (local_err) {
> +        error_propagate(errp, local_err);
> +        return -1;
> +    }
> +
> +    /*
> +     * In addition to hotplugged CPUs, send the hot-unplug notification
> +     * interrupt to the guest for coldplugged CPUs started via -device
> +     * option too.
> +     */
> +    spapr_hotplug_req_remove_by_index(drc);
> +    return 0;
> +}
> +
>  static void spapr_machine_device_unplug(HotplugHandler *hotplug_dev,
>                                        DeviceState *dev, Error **errp)
>  {
> +    sPAPRMachineClass *smc = SPAPR_MACHINE_GET_CLASS(qdev_get_machine());
> +
>      if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
>          error_setg(errp, "Memory hot unplug not supported by sPAPR");
> +    } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
> +        if (!smc->dr_cpu_enabled) {
> +            error_setg(errp, "CPU hot unplug not supported on this machine");
> +            return;
> +        }
> +        spapr_cpu_unplug(hotplug_dev, dev, errp);
>      }
>  }
>  

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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