Re: [PATCH v2 1/3] hw/i386: Initialize topo_ids from CpuInstanceProperties

[Igor Mammedov]

On Mon, 13 Jul 2020 10:02:22 -0500
Babu Moger <babu.moger@amd.com> wrote:

> > -----Original Message-----
> > From: Igor Mammedov <imammedo@redhat.com>
> > Sent: Monday, July 13, 2020 4:08 AM
> > To: Moger, Babu <Babu.Moger@amd.com>
> > Cc: pbonzini@redhat.com; rth@twiddle.net; ehabkost@redhat.com; qemu-
> > devel@nongnu.org
> > Subject: Re: [PATCH v2 1/3] hw/i386: Initialize topo_ids from
> > CpuInstanceProperties
[...]
> > > +
> > > +/*
> > > + * Initialize topo_ids from CpuInstanceProperties
> > > + * node_id in CpuInstanceProperties(or in CPU device) is a sequential
> > > + * number, but while building the topology  
> >   
> > >we need to separate it for
> > > + * each socket(mod nodes_per_pkg).  
> > could you clarify a bit more on why this is necessary?  
> 
> If you have two sockets and 4 numa nodes, node_id in CpuInstanceProperties
> will be number sequentially as 0, 1, 2, 3.  But in EPYC topology, it will
> be  0, 1, 0, 1( Basically mod % number of nodes per socket).

I'm confused, let's suppose we have 2 EPYC sockets with 2 nodes per socket
so APIC id woulbe be composed like:

 1st socket
   pkg_id(0) | node_id(0)
   pkg_id(0) | node_id(1)

 2nd socket
   pkg_id(1) | node_id(0)
   pkg_id(1) | node_id(1)
  
if that's the case, then EPYC's node_id here doesn't look like
a NUMA node in the sense it's usually used
(above config would have 4 different memory controllers => 4 conventional NUMA 
nodes).

I wonder if linux guest actually uses node_id encoded in apic id for
configuring/checking numa structures, or it just uses whatever ACPI SRAT
table provided.
 
> > > + */
> > > +static inline void x86_init_topo_ids(X86CPUTopoInfo *topo_info,
> > > +                                     CpuInstanceProperties props,
> > > +                                     X86CPUTopoIDs *topo_ids) {
> > > +    topo_ids->smt_id = props.has_thread_id ? props.thread_id : 0;
> > > +    topo_ids->core_id = props.has_core_id ? props.core_id : 0;
> > > +    topo_ids->die_id = props.has_die_id ? props.die_id : 0;
> > > +    topo_ids->node_id = props.has_node_id ?
> > > +                        props.node_id % MAX(topo_info->nodes_per_pkg, 1) 
> > > : 0;
> > > +    topo_ids->pkg_id = props.has_socket_id ? props.socket_id : 0; }
> > >  /*
> > >   * Make APIC ID for the CPU 'cpu_index'
> > >   *
> > >  
>