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

[Babu Moger]

> -----Original Message-----
> From: Igor Mammedov <imammedo@redhat.com>
> Sent: Friday, July 24, 2020 12:05 PM
> To: Moger, Babu <Babu.Moger@amd.com>
> Cc: qemu-devel@nongnu.org; pbonzini@redhat.com; ehabkost@redhat.com;
> rth@twiddle.net
> Subject: Re: [PATCH v2 1/3] hw/i386: Initialize topo_ids from
> CpuInstanceProperties
> 
> 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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.
> >
> amd.com%2Fsystem%2Ffiles%2FTechDocs%2F54945_3.03_ppr_ZP_B2_pub.zip&
> amp
> >
> ;data=02%7C01%7Cbabu.moger%40amd.com%7Ceacf7e8facbc4ae2eee808d82
> ff3ca9
> >
> 0%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C6373120714103223
> 35&amp;
> >
> sdata=%2Fdr93YVlwSq82%2FwRh2NU21Zkw4HJ%2B%2FVVYxAkhCCKJ4w%3D&a
> mp;reser
> > ved=0 (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?

Initially, I thought about it. But Intel uses die_id differently than AMD.
So, did not want complicate things.
If we take that route then we need to re-arrange the numa code as we need
to numa information to calculate the die id. So, did not want to mix up
things.

> 
> 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.

There will be complications when user configures with both die_id and
numa_id. It will complicate things further. I will have to look closely at
the code if it is feasible.

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