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

[Igor Mammedov]

On Mon, 13 Jul 2020 14:30:29 -0500
Babu Moger <babu.moger@amd.com> wrote:

> > -----Original Message-----
> > From: Igor Mammedov <imammedo@redhat.com>
> > Sent: Monday, July 13, 2020 12:32 PM
> > 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
> > 
> > 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?  
> 
> Here is the output from my EPYC machine with 2 sockets and totally 8
> nodes(SMT disabled). The cpus 0-31 are in socket 0 and  cpus 32-63 in
> socket 1.
> 
> # lscpu
> Architecture:        x86_64
> CPU op-mode(s):      32-bit, 64-bit
> Byte Order:          Little Endian
> CPU(s):              64
> On-line CPU(s) list: 0-63
> Thread(s) per core:  1
> Core(s) per socket:  32
> Socket(s):           2
> NUMA node(s):        8
> Vendor ID:           AuthenticAMD
> CPU family:          23
> Model:               1
> Model name:          AMD Eng Sample: 1S1901A4VIHF5_30/19_N
> Stepping:            2
> CPU MHz:             2379.233
> CPU max MHz:         1900.0000
> CPU min MHz:         1200.0000
> BogoMIPS:            3792.81
> Virtualization:      AMD-V
> L1d cache:           32K
> L1i cache:           64K
> L2 cache:            512K
> L3 cache:            8192K
> NUMA node0 CPU(s):   0-7
> NUMA node1 CPU(s):   8-15
> NUMA node2 CPU(s):   16-23
> NUMA node3 CPU(s):   24-31
> NUMA node4 CPU(s):   32-39
> NUMA node5 CPU(s):   40-47
> NUMA node6 CPU(s):   48-55
> NUMA node7 CPU(s):   56-63
> 
> Here is the output of #cpuid  -l 0x8000001e  -r


(1)
> You may want to refer
> https://www.amd.com/system/files/TechDocs/54945_3.03_ppr_ZP_B2_pub.zip
> (section 2.1.12.2.1.3 ApicId Enumeration Requirements).
> Note that this is a general guideline. We tried to generalize in qemu as
> much as possible. It is bit complex.


 
> CPU 0:
>    0x8000001e 0x00: eax=0x00000000 ebx=0x00000100 ecx=0x00000300
> edx=0x00000000
[...]
> CPU 63:
>    0x8000001e 0x00: eax=0x0000007e ebx=0x0000011f ecx=0x00000307
> edx=0x00000000
> 
> >   
> > >  
> > > >
> > > > 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;

It looks like I was wrong pushing system wide NUMA node-id into APIC ID
(choosen naming is confusing a bit), per [1] mentioned above, EPYC's node-id is:

• ApicId[6] = Socket ID.
* ApicId[5:4]= Node ID.
• ApicId[3] = Logical CCX L3 complex ID
• ApicId[2:0]= (SMT) ? {LogicalCoreID[1:0],ThreadId} : {1'b0,LogicalCoreID[1:0]}

which is can hold only 0-3 values, and defined as:

"A node, is an integrated circuit device that includes one to 8 cores (one or 
two Core Complexes)."

spec also mentions it indirectly as die-id if one looks at
CPUID_Fn8000001E_EBX [Core Identifiers] (Core::X86::Cpuid::CoreId)
...
  CoreId = ({2'b0, DieId[1:0], LogicalComplexId[0], LogicalThreadId[2:0]} >> SMT

and in
(2)
CPUID_Fn8000001E_ECX [Node Identifiers] (Core::X86::Cpuid::NodeId)
...
  {5'b00000,1'b[SOCKET_ID],2'b[DIE_ID]}

Question is why we did not reuse topo_ids->die_id instead of adding
confusing topo_ids->node_id in the first place?

Also looking APIC ID and SRAT table provided here,
CPUID_Fn8000001E_ECX corresponds to NUMA node id (i.e. what -numa in QEMU used 
for)
and Node ID embeded into ApicId[5:4] is basically die-id.

Difference between die-id implemented in QEMU and EPYC's die id 
(topo_ids->node_id)
is that the former doesn't require numa config (maybe it should, but 
ship'salready sailed)
and gets number of dies from '-smp dies=X' CLI option, while for EPYC we 
calculate
topo_ids->node_id implicitly from number of numa nodes and sockets, which 
implicitly
requires that machine 'must' be configured with -numa options.

Maybe we should drop this implicit calculation along with topo_ids->node_id
and reuse '-smp dies=X' plus extra checks for EPYC to ask for -numa if there
is more than 1 die and if we need to be really strict, add checks for limit of
dies/cores within socket/die according to spec[2] so encoded APIC ID and 
CPUID_8000001E
match the spec.



> > > >>>> +    topo_ids->pkg_id = props.has_socket_id ? props.socket_id :
> > > >>>> +0; }
> > > >>>>  /*
> > > >>>>   * Make APIC ID for the CPU 'cpu_index'
> > > >>>>   *
> > > >>>>  
> > > >>  
> > > >  
> > >  
> 
>