Re: [Qemu-devel] [PATCH v13 2/5] i386: Introduce auto_topoext bit to manage topoext

[Eduardo Habkost <ehabkost@redhat.com>]

On Mon, Jun 11, 2018 at 08:25:32PM +0000, Moger, Babu wrote:
> Hi Eduardo,
> Planning  to make couple of changes after testing and review.  Let me know if I missed something.
> Will wait for your feedback before the next revision.
> 
> > -----Original Message-----
> > From: kvm-owner@vger.kernel.org [mailto:kvm-owner@vger.kernel.org]
> > On Behalf Of Babu Moger
> > Sent: Friday, June 8, 2018 5:56 PM
> > To: mst@redhat.com; marcel.apfelbaum@gmail.com; pbonzini@redhat.com;
> > rth@twiddle.net; ehabkost@redhat.com; mtosatti@redhat.com
> > Cc: qemu-devel@nongnu.org; kvm@vger.kernel.org; Moger, Babu
> > <Babu.Moger@amd.com>; kash@tripleback.net; geoff@hostfission.com
> > Subject: [PATCH v13 2/5] i386: Introduce auto_topoext bit to manage
> > topoext
> > 
> > Introduce the auto_topoext bit to to control topoext feature.
> > 
> > Also add new field auto_topoext(in X86CPUDefinition). This will
> > be used to enable topoext on newer CPU models where topoext can
> > be supported.
> > 
> > Signed-off-by: Babu Moger <babu.moger@amd.com>
> > ---
> >  include/hw/i386/pc.h |  4 ++++
> >  target/i386/cpu.c    | 12 ++++++++++++
> >  target/i386/cpu.h    |  5 +++++
> >  3 files changed, 21 insertions(+)
> > 
> > diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> > index 04d1f8c..cc30ec3 100644
> > --- a/include/hw/i386/pc.h
> > +++ b/include/hw/i386/pc.h
> > @@ -303,6 +303,10 @@ bool e820_get_entry(int, uint32_t, uint64_t *,
> > uint64_t *);
> >          .driver   = TYPE_X86_CPU,\
> >          .property = "legacy-cache",\
> >          .value    = "on",\
> > +    },{\
> > +        .driver   = TYPE_X86_CPU,\
> > +        .property = "auto-topoext",\
> > +        .value    = "off",\
> >      },
> 
> We don't need this.  We are already setting this false in x86_cpu_properties.
> But we need to set it "on" for EPYC on PC_COMPAT_3_0 whenever we define it. 
> That will be a separate patch. Correct?

PC_COMPAT_3_0 will exist only on QEMU 3.1.  If you want to define
something as the default behavior in pc-3.0, just define it as
the default in the device code, which is exactly what you are
already doing in x86_cpu_load_def() below.

In other words, just set auto_topoext=true on the CPU model table
for EPYC, and it should be enough.

On PC_COMPAT_2_12, both would work:
  { TYPE_X86_CPU, "auto-topoext", "off" }
or
  { "EPYC" "-" TYPE_X86_CPU, "auto-topoext", "off" }.

I prefer the latter, but both would work.


> 
> > 
> >  #define PC_COMPAT_2_11 \
> > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > index 86fb1a4..d3411ed 100644
> > --- a/target/i386/cpu.c
> > +++ b/target/i386/cpu.c
> > @@ -1283,6 +1283,8 @@ struct X86CPUDefinition {
> >      FeatureWordArray features;
> >      const char *model_id;
> >      CPUCaches *cache_info;
> > +    /* Set it if topoext can be enabled in CPU models */
> > +    int auto_topoext;
> >  };
> > 
> >  static CPUCaches epyc_cache_info = {
> > @@ -3517,6 +3519,9 @@ static void x86_cpu_load_def(X86CPU *cpu,
> > X86CPUDefinition *def, Error **errp)
> >      /* legacy-cache defaults to 'off' if CPU model provides cache info */
> >      cpu->legacy_cache = !def->cache_info;
> > 
> > +    /* Set auto_topoext if both machine property and CPU model supports it
> > */
> > +    cpu->auto_topoext =  cpu->auto_topoext & def->auto_topoext;
> 
> This could be more appropriate like this.
> 
>  cpu->auto_topoext =  cpu->auto_topoext && def->auto_topoext;

cpu->auto_topoext is supposed to be already false, here.  Why not
just:
    cpu->auto_topoext = def->auto_topoext;
?

> 
> > +
> >      /* Special cases not set in the X86CPUDefinition structs: */
> >      /* TODO: in-kernel irqchip for hvf */
> >      if (kvm_enabled()) {
> > @@ -5382,6 +5387,13 @@ static Property x86_cpu_properties[] = {
> >      DEFINE_PROP_BOOL("legacy-cache", X86CPU, legacy_cache, true),
> > 
> >      /*
> > +     * auto-topoext property will be used to enable topoext feature.
> > +     * This will be disabled on all the older CPU models. Will be
> > +     * enabled on newer CPU modeles which can support topology extention.
> > +     */
> > +     DEFINE_PROP_BOOL("auto-topoext", X86CPU, auto_topoext, false),
> > +
> > +    /*
> >       * From "Requirements for Implementing the Microsoft
> >       * Hypervisor Interface":
> >       * https://docs.microsoft.com/en-us/virtualization/hyper-v-on-
> > windows/reference/tlfs
> > diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> > index 89c82be..8783d36 100644
> > --- a/target/i386/cpu.h
> > +++ b/target/i386/cpu.h
> > @@ -1409,6 +1409,11 @@ struct X86CPU {
> >       */
> >      bool legacy_cache;
> > 
> > +    /* Compatibility bits to enable topoext feature on all newer machines
> > +     * Disabled on older machines. Enabled on newer CPU models
> > +     */
> > +    bool auto_topoext;
> > +
> >      /* Compatibility bits for old machine types: */
> >      bool enable_cpuid_0xb;
> > 
> > --
> > 1.8.3.1
> 

-- 
Eduardo