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

[Igor Mammedov]

On Tue, 12 Jul 2016 15:07:09 +1000
David Gibson <address@hidden> wrote:

> 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 <address@hidden>
> > Signed-off-by: Bharata B Rao <address@hidden>  
> 
> After our IRC discussion last night, I prefer this version as well.
> We can definitely work with this on Power as well.
> 
> Reviewed-by: David Gibson <address@hidden>

Bharata,

Could you take this patch but strip out PC parts which were meant
as usage example only?

I'll post a separate PC patch on top of it as part of or on top of
cpu-hotplug for PC, as that series changes pc.c significantly and
resulting PC part of patch will look a bit simpler/different.

> 
> One query regarding the x86 specific implementation below, though.
> 
> > ---
> >  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;
> >      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;
> >  
> 
> Any reason not to re-use the apic_id as the migration_id?  It's 64-bit
> here which is no good, but apic_id_t is defined as uint32_t elsewhere,
> so is that just a bug with the function signature?
It could be apic_id but I chose to use possible_cpus index to make code
similar as much as possible so that when I start adding cpu-hotplug to ARM
it would be possible to reuse some of x86 code that could be generalized
shared between both archs.

> >      cpu = cpu_x86_create(cpu_model, &local_err);
> > @@ -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;
> >      pcmc->get_hotplug_handler = mc->get_hotplug_handler;
> >      pcmc->pci_enabled = true;
> >      pcmc->has_acpi_build = true;
> > diff --git a/include/hw/compat.h b/include/hw/compat.h
> > index 636befe..a66e80d 100644
> > --- a/include/hw/compat.h
> > +++ b/include/hw/compat.h
> > @@ -2,7 +2,11 @@
> >  #define HW_COMPAT_H
> >  
> >  #define HW_COMPAT_2_6 \
> > -    /* empty */
> > +    { \
> > +        .driver   = TYPE_CPU, \
> > +        .property = "use-migration-id", \
> > +        .value    = "off", \
> > +    },
> >  
> >  #define HW_COMPAT_2_5 \
> >      {\
> > diff --git a/include/qom/cpu.h b/include/qom/cpu.h
> > index 32f3af3..a29a2c9 100644
> > --- a/include/qom/cpu.h
> > +++ b/include/qom/cpu.h
> > @@ -177,6 +177,8 @@ typedef struct CPUClass {
> >                                  void *opaque);
> >  
> >      const struct VMStateDescription *vmsd;
> > +    int use_migration_id;
> > +
> >      int gdb_num_core_regs;
> >      const char *gdb_core_xml_file;
> >      gchar * (*gdb_arch_name)(CPUState *cpu);
> > @@ -360,6 +362,7 @@ 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;  
> 
> Not really in scope for this patch, but I do wonder if
> vmstate_register() should actually take a uint32_t instead of an int,
> since that's what it is on the wire, IIUC.
I think vmstate_register() uses -1 as a way to detect if it should
do instance_id auto assignment.
Any way I'll leave answer to this this question to migration experts.


> 
> >  };
> >  
> >  QTAILQ_HEAD(CPUTailQ, CPUState);
> > diff --git a/qom/cpu.c b/qom/cpu.c
> > index 751e992..3eb48b9 100644
> > --- a/qom/cpu.c
> > +++ b/qom/cpu.c
> > @@ -342,11 +342,24 @@ static int64_t cpu_common_get_arch_id(CPUState *cpu)
> >      return cpu->cpu_index;
> >  }
> >  
> > +static void cpu_common_set_use_migration_id(Object *obj, bool value,
> > +                                            Error **err)
> > +{
> > +    CPUClass *cc = CPU_GET_CLASS(obj);
> > +    cc->use_migration_id = value ? 1 : 0;
> > +}
> > +
> >  static void cpu_class_init(ObjectClass *klass, void *data)
> >  {
> >      DeviceClass *dc = DEVICE_CLASS(klass);
> >      CPUClass *k = CPU_CLASS(klass);
> >  
> > +    k->use_migration_id = -1;
> > +    object_class_property_add_bool(klass, "use-migration-id",
> > +                                   NULL,
> > +                                   cpu_common_set_use_migration_id,
> > +                                   &error_abort);
> > +
> >      k->class_by_name = cpu_common_class_by_name;
> >      k->parse_features = cpu_common_parse_features;
> >      k->reset = cpu_common_reset;  
>