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


From: Igor Mammedov
Subject: Re: [Qemu-devel] [RFC PATCH v1 2/5] cpu: Introduce CPUState::migration_id
Date: Wed, 6 Jul 2016 16:47:19 +0200

On Wed, 6 Jul 2016 19:48:03 +0530
Bharata B Rao <address@hidden> wrote:

> On Wed, Jul 06, 2016 at 01:34:59PM +0200, Igor Mammedov wrote:
> > 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.
> 
> Let me give that a try and see how it looks.
> 
> > 
> > > + * @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()
> 
> I stated with it and defined dc->props, but then felt it is a bit too
> much to define a list just for one property. But if that preferable
> let me switch back to it.
static prop is less code to maintain and not scattered all around file,
so it's more preferred if it can do the job.

> 
> Regards,
> Bharata.
> 
> 




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