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

[Igor Mammedov]

On Mon, 13 Jul 2020 11:43:33 -0500
Babu Moger <babu.moger@amd.com> wrote:

> On 7/13/20 11:17 AM, Igor Mammedov wrote:
> > 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).  
> 
> EPIC model uses combination of socket id and node id to identify the numa
> nodes. So, it internally uses all the information.

well with above values, EPYC's node_id doesn't look like it's specifying
a machine numa node, but rather a node index within single socket. In which
case, it doesn't make much sense calling it NUMA node_id, it's rather some
index within a socket. (it starts looking like terminology is all mixed up)

If you have access to a milti-socket EPYC machine, can you dump and post here
its apic ids, pls?

> 
> > 
> > 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'
> >>>>   *
> >>>>    
> >>  
> >   
>