Re: [Qemu-devel] [RFC PATCH v1 2/5] cpu: Introduce CPUState::migration_id

[Igor Mammedov]

On Wed,  6 Jul 2016 14:29:18 +0530
Bharata B Rao <address@hidden> wrote:

> Add CPUState::migration_id and use that as instance_id in
> vmstate_register() call.
> 
> Introduce use-migration-id property that allows target machines to
> optionally switch to using migration_id instead of cpu_index.
> This will help allow successful migration in cases where holes are
> introduced in cpu_index range after CPU hot removals.
> 
> The default implementation of CPUClass:get_migration_id() continues
> to return cpu_index.
> 
> Suggested-by: Igor Mammedov <address@hidden>
> Signed-off-by: Bharata B Rao <address@hidden>
> ---
>  exec.c            |  5 +++--
>  include/qom/cpu.h |  6 ++++++
>  qom/cpu.c         | 21 +++++++++++++++++++++
>  3 files changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index fb73910..a8afeda 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -619,12 +619,13 @@ static void cpu_release_index(CPUState *cpu)
>  void cpu_vmstate_register(CPUState *cpu)
>  {
>      CPUClass *cc = CPU_GET_CLASS(cpu);
> +    int instance_id = cc->get_migration_id(cpu);
>  
>      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 29ccf5c..6d00143 100644
> --- a/include/qom/cpu.h
> +++ b/include/qom/cpu.h
> @@ -187,6 +187,7 @@ typedef struct CPUClass {
>      bool (*cpu_exec_interrupt)(CPUState *cpu, int interrupt_request);
>  
>      void (*disas_set_info)(CPUState *cpu, disassemble_info *info);
> +    int (*get_migration_id)(CPUState *cpu);
>  } CPUClass;
>  
>  #ifdef HOST_WORDS_BIGENDIAN
> @@ -273,6 +274,9 @@ 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.
> + * @migration_id: Use as instance_id argument in cpu
> vmstate_register calls
with this field get_migration_id() callback is redundant.
You can drop get_migration_id() and assign value to migration_id in
machine specific code /spapr/ppc/x86/.../ before realize is called.
That should simplify this patch and its users as well.

> + * @use_migration_id: Set to enforce the use of
> CPUClass.get_migration_id()
> + *     over cpu_index during vmstate registration.
>   *
>   * State of one CPU core or thread.
>   */
> @@ -360,6 +364,8 @@ 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 migration_id;
> +    bool use_migration_id;
>  };
>  
>  QTAILQ_HEAD(CPUTailQ, CPUState);
> diff --git a/qom/cpu.c b/qom/cpu.c
> index 488ecc6..01cf136 100644
> --- a/qom/cpu.c
> +++ b/qom/cpu.c
> @@ -326,6 +326,17 @@ static void cpu_common_realizefn(DeviceState
> *dev, Error **errp) }
>  }
>  
> +static bool cpu_common_get_use_migration_id(Object *obj, Error
> **errp) +{
> +    return CPU(obj)->use_migration_id;
> +}
> +
> +static void cpu_common_set_use_migration_id(Object *obj, bool value,
> +                                            Error **err)
> +{
> +    CPU(obj)->use_migration_id = value;
> +}
It's possible to create dumb property in a more compact way,
see DEFINE_PROP_BOOL()


>  static void cpu_common_initfn(Object *obj)
>  {
>      CPUState *cpu = CPU(obj);
> @@ -336,6 +347,10 @@ static void cpu_common_initfn(Object *obj)
>      qemu_mutex_init(&cpu->work_mutex);
>      QTAILQ_INIT(&cpu->breakpoints);
>      QTAILQ_INIT(&cpu->watchpoints);
> +
> +    object_property_add_bool(obj, "use-migration-id",
> +                             cpu_common_get_use_migration_id,
> +                             cpu_common_set_use_migration_id, NULL);
>  }
>  
>  static void cpu_common_finalize(Object *obj)
> @@ -348,6 +363,11 @@ static int64_t cpu_common_get_arch_id(CPUState
> *cpu) return cpu->cpu_index;
>  }
>  
> +static int cpu_common_get_migration_id(CPUState *cpu)
> +{
> +    return cpu->cpu_index;
> +}
> +
>  static void cpu_class_init(ObjectClass *klass, void *data)
>  {
>      DeviceClass *dc = DEVICE_CLASS(klass);
> @@ -372,6 +392,7 @@ static void cpu_class_init(ObjectClass *klass,
> void *data) k->cpu_exec_enter = cpu_common_noop;
>      k->cpu_exec_exit = cpu_common_noop;
>      k->cpu_exec_interrupt = cpu_common_exec_interrupt;
> +    k->get_migration_id = cpu_common_get_migration_id;
>      dc->realize = cpu_common_realizefn;
>      dc->unrealize = cpu_common_unrealizefn;
>      /*