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

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

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On Thu, Jul 07, 2016 at 07:52:32PM +0200, Greg Kurz wrote:
> 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.

No.. it really does.  The ids need to exactly match, not just be in
the same range in order to maintain migration compatibility with
pre-stable_cpu_id versions of qemu.

> 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 = {
> 

-- 
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

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