Re: [Qemu-devel] [for-2.7 PATCH v3 12/15] spapr: CPU hot unplug support

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

[-- Attachment #1: Type: text/plain, Size: 6888 bytes --]

On Thu, May 12, 2016 at 09:18:22AM +0530, Bharata B Rao wrote:
> Remove the CPU core device by removing the underlying CPU thread devices.
> Hot removal of CPU for sPAPR guests is achieved by sending the hot unplug
> notification to the guest. 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>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

Couple of suggestions for minor improvements below, though.

> ---
>  hw/ppc/spapr.c                  | 16 ++++++++
>  hw/ppc/spapr_cpu_core.c         | 81 +++++++++++++++++++++++++++++++++++++++++
>  include/hw/ppc/spapr.h          |  1 +
>  include/hw/ppc/spapr_cpu_core.h | 11 ++++++
>  4 files changed, 109 insertions(+)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 8c3100d..a8cd74d 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -2342,11 +2342,27 @@ static void spapr_machine_device_plug(HotplugHandler *hotplug_dev,
>      }
>  }
>  
> +void spapr_cpu_destroy(PowerPCCPU *cpu)

I think this would make more sense in spapr_cpu_core.c (where it could
be static).

> +{
> +    sPAPRMachineState *spapr = SPAPR_MACHINE(qdev_get_machine());
> +
> +    xics_cpu_destroy(spapr->icp, cpu);
> +    qemu_unregister_reset(spapr_cpu_reset, cpu);
> +}
> +
>  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_SPAPR_CPU_CORE)) {
> +        if (!smc->dr_cpu_enabled) {
> +            error_setg(errp, "CPU hot unplug not supported on this machine");
> +            return;
> +        }
> +        spapr_core_unplug(hotplug_dev, dev, errp);
>      }
>  }
>  
> diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> index ed36beb..0b62456 100644
> --- a/hw/ppc/spapr_cpu_core.c
> +++ b/hw/ppc/spapr_cpu_core.c
> @@ -28,6 +28,87 @@ char *spapr_get_cpu_core_type(const char *model)
>      return g_strdup(core_type);
>  }
>  
> +static void spapr_cpu_core_cleanup(struct sPAPRCPUUnplugList *unplug_list)
> +{
> +    sPAPRCPUUnplug *unplug, *next;
> +    Object *cpu;
> +
> +    QLIST_FOREACH_SAFE(unplug, unplug_list, node, next) {
> +        cpu = unplug->cpu;
> +        object_unparent(cpu);
> +        QLIST_REMOVE(unplug, node);
> +        g_free(unplug);
> +    }
> +}
> +
> +static void spapr_add_cpu_to_unplug_list(Object *cpu,
> +                                         struct sPAPRCPUUnplugList *unplug_list)
> +{
> +    sPAPRCPUUnplug *unplug = g_malloc(sizeof(*unplug));
> +
> +    unplug->cpu = cpu;
> +    QLIST_INSERT_HEAD(unplug_list, unplug, node);
> +}
> +
> +static int spapr_cpu_release(Object *obj, void *opaque)
> +{
> +    DeviceState *dev = DEVICE(obj);
> +    CPUState *cs = CPU(dev);
> +    PowerPCCPU *cpu = POWERPC_CPU(cs);
> +    struct sPAPRCPUUnplugList *unplug_list = opaque;
> +
> +    spapr_cpu_destroy(cpu);
> +    cpu_remove_sync(cs);
> +
> +    /*
> +     * We are still walking the core object's children list, and
> +     * hence can't cleanup this CPU thread object just yet. Put
> +     * it on a list for later removal.
> +     */
> +    spapr_add_cpu_to_unplug_list(obj, unplug_list);
> +    return 0;
> +}
> +
> +static void spapr_core_release(DeviceState *dev, void *opaque)
> +{
> +    struct sPAPRCPUUnplugList unplug_list;
> +    sPAPRMachineState *spapr = SPAPR_MACHINE(qdev_get_machine());
> +    sPAPRCPUCore *core = SPAPR_CPU_CORE(OBJECT(dev));
> +    CPUCore *cc = CPU_CORE(dev);
> +    int smt = kvmppc_smt_threads();
> +
> +    QLIST_INIT(&unplug_list);
> +    object_child_foreach(OBJECT(dev), spapr_cpu_release, &unplug_list);
> +    spapr_cpu_core_cleanup(&unplug_list);
> +    spapr->cores[cc->core / smt] = NULL;

Could you avoid the awkwardness with the two phase release by stepping
through the cc->threads array instead of using object_child_foreach()?

> +
> +    g_free(core->threads);
> +    object_unparent(OBJECT(dev));
> +}
> +
> +void spapr_core_unplug(HotplugHandler *hotplug_dev, DeviceState *dev,
> +                       Error **errp)
> +{
> +    sPAPRCPUCore *core = SPAPR_CPU_CORE(OBJECT(dev));
> +    PowerPCCPU *cpu = &core->threads[0];
> +    int id = ppc_get_vcpu_dt_id(cpu);
> +    sPAPRDRConnector *drc =
> +        spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_CPU, id);
> +    sPAPRDRConnectorClass *drck;
> +    Error *local_err = NULL;
> +
> +    g_assert(drc);
> +
> +    drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
> +    drck->detach(drc, dev, spapr_core_release, NULL, &local_err);
> +    if (local_err) {
> +        error_propagate(errp, local_err);
> +        return;
> +    }
> +
> +    spapr_hotplug_req_remove_by_index(drc);
> +}
> +
>  void spapr_core_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
>                       Error **errp)
>  {
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index ca4ae3e..a443693 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -585,6 +585,7 @@ void spapr_hotplug_req_remove_by_count(sPAPRDRConnectorType drc_type,
>  void spapr_cpu_init(sPAPRMachineState *spapr, PowerPCCPU *cpu, Error **errp);
>  void *spapr_populate_hotplug_cpu_dt(CPUState *cs, int *fdt_offset,
>                                      sPAPRMachineState *spapr);
> +void spapr_cpu_destroy(PowerPCCPU *cpu);
>  
>  /* rtas-configure-connector state */
>  struct sPAPRConfigureConnectorState {
> diff --git a/include/hw/ppc/spapr_cpu_core.h b/include/hw/ppc/spapr_cpu_core.h
> index 4cd837e..3d8d6ac 100644
> --- a/include/hw/ppc/spapr_cpu_core.h
> +++ b/include/hw/ppc/spapr_cpu_core.h
> @@ -30,4 +30,15 @@ void spapr_core_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
>  char *spapr_get_cpu_core_type(const char *model);
>  void spapr_core_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
>                       Error **errp);
> +void spapr_core_unplug(HotplugHandler *hotplug_dev, DeviceState *dev,
> +                       Error **errp);
> +
> +/* List to store unplugged CPU objects for cleanup during unplug */
> +typedef struct sPAPRCPUUnplug {
> +    Object *cpu;
> +    QLIST_ENTRY(sPAPRCPUUnplug) node;
> +} sPAPRCPUUnplug;
> +
> +QLIST_HEAD(sPAPRCPUUnplugList, sPAPRCPUUnplug);
> +
>  #endif

-- 
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

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 819 bytes --]