Re: [Qemu-devel] [PATCH] VARIANT 1: reuse device compat logic to pick preffered CPU's migration instance_id

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Mon, Jul 11, 2016 at 03:42:29PM +0200, Igor Mammedov wrote:
> this approach i I preffer as it uses less per machine migration glue
> and follows typical compat pattern for devices
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> ---
>  exec.c              |  7 +++++--
>  hw/i386/pc.c        | 10 +++++++---
>  include/hw/compat.h |  6 +++++-
>  include/qom/cpu.h   |  3 +++
>  qom/cpu.c           | 13 +++++++++++++
>  5 files changed, 33 insertions(+), 6 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 0122ef7..79e1dcb 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -670,6 +670,7 @@ void cpu_exec_init(CPUState *cpu, Error **errp)
>  {
>      CPUClass *cc = CPU_GET_CLASS(cpu);
>      Error *local_err = NULL;
> +    int migration_id;
> 
>      cpu->as = NULL;
>      cpu->num_ases = 0;
> @@ -708,11 +709,13 @@ void cpu_exec_init(CPUState *cpu, Error **errp)
>      (void) cc;
>      cpu_list_unlock();
>  #else
> +    migration_id = cc->use_migration_id > 0 ?
> +        cpu->migration_id : cpu->cpu_index;

cc->use_migration_id is always -1 here (See explanation below)

>      if (qdev_get_vmsd(DEVICE(cpu)) == NULL) {
> -        vmstate_register(NULL, cpu->cpu_index, &vmstate_cpu_common, cpu);
> +        vmstate_register(NULL, migration_id, &vmstate_cpu_common, cpu);
>      }
>      if (cc->vmsd != NULL) {
> -        vmstate_register(NULL, cpu->cpu_index, cc->vmsd, cpu);
> +        vmstate_register(NULL, migration_id, cc->vmsd, cpu);
>      }
>  #endif
>  }
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index cd1745e..f041279 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1040,9 +1040,10 @@ void pc_acpi_smi_interrupt(void *opaque, int irq, int level)
>  }
> 
>  static X86CPU *pc_new_cpu(const char *cpu_model, int64_t apic_id,
> -                          Error **errp)
> +                          Error **errp, int migration_id)
>  {
>      X86CPU *cpu = NULL;
> +    CPUState *cs = CPU(cpu);
>      Error *local_err = NULL;
> 
>      cpu = cpu_x86_create(cpu_model, &local_err);

Assignment to cs should move here after cpu_x86_create.

> @@ -1050,6 +1051,7 @@ static X86CPU *pc_new_cpu(const char *cpu_model, int64_t apic_id,
>          goto out;
>      }
> 
> +    cs->migration_id = migration_id;
>      object_property_set_int(OBJECT(cpu), apic_id, "apic-id", &local_err);
>      object_property_set_bool(OBJECT(cpu), true, "realized", &local_err);
> 
> @@ -1093,7 +1095,7 @@ void pc_hot_add_cpu(const int64_t id, Error **errp)
>          return;
>      }
> 
> -    cpu = pc_new_cpu(machine->cpu_model, apic_id, &local_err);
> +    cpu = pc_new_cpu(machine->cpu_model, apic_id, &local_err, id);
>      if (local_err) {
>          error_propagate(errp, local_err);
>          return;
> @@ -1137,7 +1139,7 @@ void pc_cpus_init(PCMachineState *pcms)
>          pcms->possible_cpus->len++;
>          if (i < smp_cpus) {
>              cpu = pc_new_cpu(machine->cpu_model, x86_cpu_apic_id_from_index(i),
> -                             &error_fatal);
> +                             &error_fatal, i);
>              pcms->possible_cpus->cpus[i].cpu = CPU(cpu);
>              object_unref(OBJECT(cpu));
>          }
> @@ -2012,7 +2014,9 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
>      PCMachineClass *pcmc = PC_MACHINE_CLASS(oc);
>      HotplugHandlerClass *hc = HOTPLUG_HANDLER_CLASS(oc);
>      NMIClass *nc = NMI_CLASS(oc);
> +    CPUClass *cc = CPU_CLASS(object_class_by_name(TYPE_CPU));
> 
> +    cc->use_migration_id = true;

It is not clear as to how setting cc->use_migration_id here in machine class
init would affect all CPUs. What I am observing is that the cc that we
set here is different from the cc that we get via GET_CPU_CLASS(cpu) in
cpu_exec_init(). Hence use_migration_id is never set for any CPUs that
get created.

Regards,
Bharata.