Re: [Qemu-devel] [RFC PATCH v0 1/1] spapr: Support setting of compat CPU type for CPU cores

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

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On Wed, Jun 22, 2016 at 08:06:50AM +0530, Bharata B Rao wrote:
> On Tue, Jun 21, 2016 at 03:10:00PM +1000, David Gibson wrote:
> > On Sat, Jun 18, 2016 at 02:04:06PM +0530, Bharata B Rao wrote:
> > > Compat CPU type is typically specified on -cpu cmdline option like:
> > > -cpu host,compat=power7 or -cpu POWER8E,compat=power7 etc.
> > > With the introduction of sPAPR CPU core devices, we need to support
> > > the same for core devices too.
> > > 
> > > Support the specification of CPU compat type on device_add command for
> > > sPAPRCPUCore devices like:
> > > (qemu) device_add POWER8E-spapr-cpu-core,id=core3,compat=power7,core-id=24
> > > 
> > > Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> > > ---
> > > Applies on ppc-for-2.7 branch of David Gibson's tree.
> > 
> > The implementation looks ok apart from a few nits noted below.
> > 
> > There's a larger problem here, though, in that this doesn't advertise
> > the necessary compat= property via query-hotpluggable-cpus qmp and hmp
> > interfaces.  Which means that management has no good way of knowing
> > it's necessary.
> > 
> > > 
> > >  hw/ppc/spapr.c                  |  8 +++++
> > >  hw/ppc/spapr_cpu_core.c         | 73 +++++++++++++++++++++++++++++++++++++++++
> > >  include/hw/ppc/spapr_cpu_core.h |  2 ++
> > >  3 files changed, 83 insertions(+)
> > > 
> > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > > index 778fa25..2049d7d 100644
> > > --- a/hw/ppc/spapr.c
> > > +++ b/hw/ppc/spapr.c
> > > @@ -1807,6 +1807,7 @@ static void ppc_spapr_init(MachineState *machine)
> > >              if (i < spapr_cores) {
> > >                  char *type = spapr_get_cpu_core_type(machine->cpu_model);
> > >                  Object *core;
> > > +                char *compat;
> > >  
> > >                  if (!object_class_by_name(type)) {
> > >                      error_report("Unable to find sPAPR CPU Core definition");
> > > @@ -1818,6 +1819,13 @@ static void ppc_spapr_init(MachineState *machine)
> > >                                          &error_fatal);
> > >                  object_property_set_int(core, core_dt_id, CPU_CORE_PROP_CORE_ID,
> > >                                          &error_fatal);
> > > +                compat = spapr_get_cpu_compat_type(machine->cpu_model);
> > > +                if (compat) {
> > > +                    object_property_set_str(core, compat, "compat",
> > > +                                            &error_fatal);
> > > +                    g_free(compat);
> > > +                }
> > > +
> > >                  object_property_set_bool(core, true, "realized", &error_fatal);
> > >              }
> > >          }
> > > diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> > > index 3a5da09..9eb63cc 100644
> > > --- a/hw/ppc/spapr_cpu_core.c
> > > +++ b/hw/ppc/spapr_cpu_core.c
> > > @@ -96,6 +96,24 @@ char *spapr_get_cpu_core_type(const char *model)
> > >      return core_type;
> > >  }
> > >  
> > > +/*
> > > + * Returns the CPU compat type specified in -cpu @model.
> > > + */
> > > +char *spapr_get_cpu_compat_type(const char *model)
> > > +{
> > > +    char *compat_type = NULL;
> > > +    gchar **model_pieces = g_strsplit(model, ",", 2);
> > > +
> > > +    if (model_pieces[1]) {
> > > +        gchar **compat_pieces = g_strsplit(model_pieces[1], "=", 2);
> > > +
> > > +        compat_type = g_strdup_printf("%s", compat_pieces[1]);
> > > +    }
> > > +
> > > +    g_strfreev(model_pieces);
> > > +    return compat_type;
> > > +}
> > > +
> > >  static void spapr_core_release(DeviceState *dev, void *opaque)
> > >  {
> > >      sPAPRCPUCore *sc = SPAPR_CPU_CORE(OBJECT(dev));
> > > @@ -223,12 +241,31 @@ void spapr_core_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
> > >      CPUCore *cc = CPU_CORE(dev);
> > >      char *base_core_type = spapr_get_cpu_core_type(machine->cpu_model);
> > >      const char *type = object_get_typename(OBJECT(dev));
> > > +    char *base_compat_type = NULL;
> > > +    char *compat = NULL;
> > > +    bool compat_set;
> > >  
> > >      if (strcmp(base_core_type, type)) {
> > >          error_setg(&local_err, "CPU core type should be %s", base_core_type);
> > >          goto out;
> > >      }
> > >  
> > > +    base_compat_type = spapr_get_cpu_compat_type(machine->cpu_model);
> > 
> > This can go in the initializer to match the base_core_type.
> 
> Had it that way, but since there was an error exit possibility when
> base_core_type is not matching, I thought better to initialize base_compat_type
> after that check.

Ah, good point.  I forgot that get_cpu_compat_type() had an implicit
allocation that needs cleanup.

> > > @@ -298,9 +339,19 @@ static void spapr_cpu_core_realize(DeviceState *dev, Error **errp)
> > >          snprintf(id, sizeof(id), "thread[%d]", i);
> > >          object_property_add_child(OBJECT(sc), id, obj, &local_err);
> > >          if (local_err) {
> > > +            g_free(compat);
> > >              goto err;
> > >          }
> > > +        if (compat_set) {
> > > +            CPUClass *cc = CPU_GET_CLASS(CPU(obj));
> > > +            char *featurestr = g_strdup_printf("compat=%s", compat);
> > > +
> > > +            cc->parse_features(CPU(obj), featurestr, &local_err);
> > 
> > Hmm.. would it make more sense to just do an object_property_set()
> > rather than calling into parse_features?
> 
> It would work, but I guess better to use ->parse_features() to ensure
> future additional properties would work seamlessly.

Hmm.. except that the string you're forming to pass to parse_features
is always just "compat=%s".  So you'd have to change that bit anyway,
so I don't see that using parse_features really buys you anything.

-- 
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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