Re: [Qemu-devel] [PATCH v13 4/5] i386: Verify and enable topoext feature if supported

[Moger, Babu]

> -----Original Message-----
> From: address@hidden [mailto:address@hidden
> On Behalf Of Eduardo Habkost
> Sent: Monday, June 11, 2018 3:52 PM
> To: Moger, Babu <address@hidden>
> Cc: address@hidden; address@hidden; address@hidden;
> address@hidden; address@hidden; address@hidden;
> address@hidden; address@hidden; address@hidden
> Subject: Re: [PATCH v13 4/5] i386: Verify and enable topoext feature if
> supported
> 
> On Fri, Jun 08, 2018 at 06:56:20PM -0400, Babu Moger wrote:
> > If the CPU model supports topoext feature, enabled the
> > feature automatically if it can be supported.
> >
> > Signed-off-by: Babu Moger <address@hidden>
> > ---
> >  target/i386/cpu.c | 40 ++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 40 insertions(+)
> >
> > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > index 4dd9a82..88bc73d 100644
> > --- a/target/i386/cpu.c
> > +++ b/target/i386/cpu.c
> > @@ -4763,6 +4763,33 @@ static int x86_cpu_filter_features(X86CPU *cpu)
> >  #define IS_AMD_CPU(env) ((env)->cpuid_vendor1 ==
> CPUID_VENDOR_AMD_1 && \
> >                           (env)->cpuid_vendor2 == CPUID_VENDOR_AMD_2 && \
> >                           (env)->cpuid_vendor3 == CPUID_VENDOR_AMD_3)
> > +/*
> > + * Check if we can support this topology
> > + * Fail if number of cores are beyond the supported config
> > + * or nr_threads is more than 2
> > + */
> > +static int topology_supports_topoext(int nr_cores, int nr_threads,
> > +            Error **errp)
> > +{
> > +    if (nr_cores > (MAX_CORES_IN_NODE * MAX_NODES_PER_SOCKET)) {
> > +        error_setg(errp, "TOPOEXT unsupported with %d cores per socket",
> > +                   nr_cores);
> > +        error_append_hint(errp, "TOPOEXT supports only up to %d cores
> per"
> > +                          " socket\n",
> > +                          (MAX_CORES_IN_NODE * MAX_NODES_PER_SOCKET));
> > +        return false;
> > +    }
> > +
> > +    if (nr_threads > 2) {
> > +        error_setg(errp, "TOPOEXT unsupported with %d threads per core",
> > +                   nr_threads);
> > +        error_append_hint(errp, "TOPOEXT supports only up to 2 threads"
> > +                          " per core\n");
> > +        return false;
> > +    }
> > +    return true;
> > +}
> > +
> >  static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
> >  {
> >      CPUState *cs = CPU(dev);
> > @@ -4953,6 +4980,19 @@ static void x86_cpu_realizefn(DeviceState *dev,
> Error **errp)
> >
> >      qemu_init_vcpu(cs);
> >
> > +    if (cpu->auto_topoext &&
> > +        !(env->user_features[FEAT_8000_0001_ECX] &
> CPUID_EXT3_TOPOEXT)) {
> > +        if (cs->nr_cores <= (MAX_CORES_IN_NODE *
> MAX_NODES_PER_SOCKET) &&
> > +            (cs->nr_threads <= 2)) {
> 
> This duplicates the logic from topology_supports_topoext().  Why
> not just call
>   topology_supports_topoext(cs->nr_cores, cs->nr_threads, NULL)
> here?

Ok. Will do it.

> 
> > +            env->features[FEAT_8000_0001_ECX] |= CPUID_EXT3_TOPOEXT;
> > +        }
> > +    }
> > +
> > +    if ((env->features[FEAT_8000_0001_ECX] & CPUID_EXT3_TOPOEXT) &&
> > +        !topology_supports_topoext(cs->nr_cores, cs->nr_threads, errp)) {
> > +        return;
> > +    }
> > +
> >      /* Only Intel CPUs support hyperthreading. Even though QEMU fixes this
> >       * issue by adjusting CPUID_0000_0001_EBX and CPUID_8000_0008_ECX
> >       * based on inputs (sockets,cores,threads), it is still better to gives
> > --
> > 1.8.3.1
> >
> 
> --
> Eduardo