Re: [Qemu-devel] [RFC PATCH v2 2/5] cpu: Introduce CPUState::stable_cpu_id

[Greg Kurz <groug@kaod.org>]

On Thu,  7 Jul 2016 20:20:22 +0530
Bharata B Rao <bharata@linux.vnet.ibm.com> wrote:

> Add CPUState::stable_cpu_id and use that as instance_id in
> vmstate_register() call.
> 
> Introduce has-stable_cpu_id property that allows target machines to
> optionally switch to using stable_cpu_id instead of cpu_index.

If stable_cpu_id is in the [0..max_vcpus) range, then it does not really depend
on the machine type or version. In this case, the property is not needed.

> This will help allow successful migration in cases where holes are
> introduced in cpu_index range after CPU hot removals.
> 
> Suggested-by: Igor Mammedov <imammedo@redhat.com>
> Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> ---
>  exec.c            | 6 ++++--
>  include/qom/cpu.h | 5 +++++
>  qom/cpu.c         | 6 ++++++
>  3 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index fb73910..3b36fe5 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -619,12 +619,14 @@ static void cpu_release_index(CPUState *cpu)
>  void cpu_vmstate_register(CPUState *cpu)
>  {
>      CPUClass *cc = CPU_GET_CLASS(cpu);
> +    int instance_id = cpu->has_stable_cpu_id ? cpu->stable_cpu_id :
> +                      cpu->cpu_index;
>  
>      if (qdev_get_vmsd(DEVICE(cpu)) == NULL) {
> -        vmstate_register(NULL, cpu->cpu_index, &vmstate_cpu_common, cpu);
> +        vmstate_register(NULL, instance_id, &vmstate_cpu_common, cpu);
>      }
>      if (cc->vmsd != NULL) {
> -        vmstate_register(NULL, cpu->cpu_index, cc->vmsd, cpu);
> +        vmstate_register(NULL, instance_id, cc->vmsd, cpu);
>      }
>  }
>  
> diff --git a/include/qom/cpu.h b/include/qom/cpu.h
> index 331386f..527c021 100644
> --- a/include/qom/cpu.h
> +++ b/include/qom/cpu.h
> @@ -273,6 +273,9 @@ struct qemu_work_item {
>   * @kvm_fd: vCPU file descriptor for KVM.
>   * @work_mutex: Lock to prevent multiple access to queued_work_*.
>   * @queued_work_first: First asynchronous work pending.
> + * @stable_cpu_id: Use as instance_id argument in cpu vmstate_register calls
> + * @has_stable_cpu_id: Set to enforce the use of @stable_cpu_id
> + *     over cpu_index during vmstate registration.
>   *
>   * State of one CPU core or thread.
>   */
> @@ -360,6 +363,8 @@ struct CPUState {
>         (absolute value) offset as small as possible.  This reduces code
>         size, especially for hosts without large memory offsets.  */
>      uint32_t tcg_exit_req;
> +    int stable_cpu_id;
> +    bool has_stable_cpu_id;
>  };
>  
>  QTAILQ_HEAD(CPUTailQ, CPUState);
> diff --git a/qom/cpu.c b/qom/cpu.c
> index 1095ea1..bae1bf7 100644
> --- a/qom/cpu.c
> +++ b/qom/cpu.c
> @@ -363,6 +363,11 @@ static int64_t cpu_common_get_arch_id(CPUState *cpu)
>      return cpu->cpu_index;
>  }
>  
> +static Property cpu_common_properties[] = {
> +    DEFINE_PROP_BOOL("has-stable-cpu-id", CPUState, has_stable_cpu_id, false),
> +    DEFINE_PROP_END_OF_LIST()
> +};
> +
>  static void cpu_class_init(ObjectClass *klass, void *data)
>  {
>      DeviceClass *dc = DEVICE_CLASS(klass);
> @@ -394,6 +399,7 @@ static void cpu_class_init(ObjectClass *klass, void *data)
>       * IRQs, adding reset handlers, halting non-first CPUs, ...
>       */
>      dc->cannot_instantiate_with_device_add_yet = true;
> +    dc->props = cpu_common_properties;
>  }
>  
>  static const TypeInfo cpu_type_info = {