Re: [Qemu-devel] [RFC 1/3] target-i386: moving registers of vmstate from cpu_exec_init() to x86_cpu_realizefn()

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 15 Jan 2014 20:24:01 +0800
Chen Fan <chen.fan.fnst@cn.fujitsu.com> wrote:

> On Tue, 2014-01-14 at 11:40 +0100, Igor Mammedov wrote:
> > On Tue, 14 Jan 2014 17:27:20 +0800
> > Chen Fan <chen.fan.fnst@cn.fujitsu.com> wrote:
> > 
> > > the intend of this patch is to register cpu vmstates with apic id instead of cpu
> > > index, due to the property setting of apic_id is behind the cpu initialization. so
> > > we move the registers of cpu vmstate from cpu_exec_init() to x86_cpu_realizefn() to
> > > let the set apicid as the parameter.
> > > 
> > > Signed-off-by: Chen Fan <chen.fan.fnst@cn.fujitsu.com>
> > > ---
> > >  exec.c            | 5 +++++
> > >  target-i386/cpu.c | 9 +++++++++
> > >  2 files changed, 14 insertions(+)
> > > 
> > > diff --git a/exec.c b/exec.c
> > > index 7e49e8e..9be5855 100644
> > > --- a/exec.c
> > > +++ b/exec.c
> > > @@ -438,7 +438,9 @@ CPUState *qemu_get_cpu(int index)
> > >  void cpu_exec_init(CPUArchState *env)
> > >  {
> > >      CPUState *cpu = ENV_GET_CPU(env);
> > > +#if !defined(TARGET_I386)
> > >      CPUClass *cc = CPU_GET_CLASS(cpu);
> > > +#endif
> > >      CPUState *some_cpu;
> > >      int cpu_index;
> > >  
> > > @@ -460,6 +462,8 @@ void cpu_exec_init(CPUArchState *env)
> > >  #if defined(CONFIG_USER_ONLY)
> > >      cpu_list_unlock();
> > >  #endif
> > > +
> > > +#if !defined(TARGET_I386)
> > >      if (qdev_get_vmsd(DEVICE(cpu)) == NULL) {
> > >          vmstate_register(NULL, cpu_index, &vmstate_cpu_common, cpu);
> > >      }
> > > @@ -472,6 +476,7 @@ void cpu_exec_init(CPUArchState *env)
> > >      if (cc->vmsd != NULL) {
> > >          vmstate_register(NULL, cpu_index, cc->vmsd, cpu);
> > >      }
> > > +#endif /* !TARGET_I386 */
> > >  }
> > >  
> > >  #if defined(TARGET_HAS_ICE)
> > > diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> > > index 967529a..dada6f6 100644
> > > --- a/target-i386/cpu.c
> > > +++ b/target-i386/cpu.c
> > > @@ -2552,6 +2552,7 @@ static void x86_cpu_apic_realize(X86CPU *cpu, Error **errp)
> > >  static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
> > >  {
> > >      CPUState *cs = CPU(dev);
> > > +    CPUClass *cc = CPU_GET_CLASS(cs);
> > >      X86CPU *cpu = X86_CPU(dev);
> > >      X86CPUClass *xcc = X86_CPU_GET_CLASS(dev);
> > >      CPUX86State *env = &cpu->env;
> > > @@ -2615,6 +2616,14 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
> > >      cpu_reset(cs);
> > >  
> > >      xcc->parent_realize(dev, &local_err);
> > > +
> > > +    if (qdev_get_vmsd(DEVICE(cs)) == NULL) {
> > > +        vmstate_register(NULL, env->cpuid_apic_id, &vmstate_cpu_common, cs);
> > > +    }
> > > +
> > > +    if (cc->vmsd != NULL) {
> > > +        vmstate_register(NULL, env->cpuid_apic_id, cc->vmsd, cs);
> > > +    }
> > how about doing it in common CPUclass.realize()
> > you can use get_arch_id() for getting CPU id, it returns cpu_index by default
> > and apic_id for target-i386.
> 
> Thanks for your kind suggestion, does this mean we can directly move
> vmstate_register to cpu_common_realizefn()? 
yep, that is a gist of it.

There is more to the issue with discontinuous CPUs, a lot of code still
use cpu_index and the way it's allocated is not compatible with discontinuous
CPUs, so this issue should be fixed as well.

Also you propose to use a raw apic id with CLI/user interface.
I recall there were objections to it since APIC ID contains topology
information and it's not trivial for user to get it right.
The last idea that was discussed to fix it was not expose APIC ID to
user but rather introduce QOM hierarchy like:
  /machine/node/N/socket/X/core/Y/thread/Z
and use it in user interface as a means to specify an arbitrary CPU
and let QEMU calculate APIC ID based on this path.

But nobody took on implementing it yet.

CCing Eduardo as hi might be interested in this as well.

> 
> > Pls note that changing vmstate id should be done only for new machine types
> > so not to break old qemu -> new qemu migration.
> Yes.
> 
> Thanks.
> Chen
> 
> > 
> > >  out:
> > >      if (local_err != NULL) {
> > >          error_propagate(errp, local_err);
> > 
> > 
> 
> 


-- 
Regards,
  Igor