Re: [PATCH v3 1/4] hw/arm/virt: Consider SMP configuration in CPU topology

[Igor Mammedov]

On Sat, 26 Mar 2022 02:49:59 +0800
Gavin Shan <gshan@redhat.com> wrote:

> Hi Igor,
> 
> On 3/25/22 9:19 PM, Igor Mammedov wrote:
> > On Wed, 23 Mar 2022 15:24:35 +0800
> > Gavin Shan <gshan@redhat.com> wrote:  
> >> Currently, the SMP configuration isn't considered when the CPU
> >> topology is populated. In this case, it's impossible to provide
> >> the default CPU-to-NUMA mapping or association based on the socket
> >> ID of the given CPU.
> >>
> >> This takes account of SMP configuration when the CPU topology
> >> is populated. The die ID for the given CPU isn't assigned since
> >> it's not supported on arm/virt machine yet. Besides, the cluster
> >> ID for the given CPU is assigned because it has been supported
> >> on arm/virt machine.
> >>
> >> Signed-off-by: Gavin Shan <gshan@redhat.com>
> >> ---
> >>   hw/arm/virt.c     | 11 +++++++++++
> >>   qapi/machine.json |  6 ++++--
> >>   2 files changed, 15 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> >> index d2e5ecd234..064eac42f7 100644
> >> --- a/hw/arm/virt.c
> >> +++ b/hw/arm/virt.c
> >> @@ -2505,6 +2505,7 @@ static const CPUArchIdList 
> >> *virt_possible_cpu_arch_ids(MachineState *ms)
> >>       int n;
> >>       unsigned int max_cpus = ms->smp.max_cpus;
> >>       VirtMachineState *vms = VIRT_MACHINE(ms);
> >> +    MachineClass *mc = MACHINE_GET_CLASS(vms);
> >>   
> >>       if (ms->possible_cpus) {
> >>           assert(ms->possible_cpus->len == max_cpus);
> >> @@ -2518,6 +2519,16 @@ static const CPUArchIdList 
> >> *virt_possible_cpu_arch_ids(MachineState *ms)
> >>           ms->possible_cpus->cpus[n].type = ms->cpu_type;
> >>           ms->possible_cpus->cpus[n].arch_id =
> >>               virt_cpu_mp_affinity(vms, n);
> >> +
> >> +        assert(!mc->smp_props.dies_supported);
> >> +        ms->possible_cpus->cpus[n].props.has_socket_id = true;
> >> +        ms->possible_cpus->cpus[n].props.socket_id =
> >> +            n / (ms->smp.clusters * ms->smp.cores * ms->smp.threads);
> >> +        ms->possible_cpus->cpus[n].props.has_cluster_id = true;
> >> +        ms->possible_cpus->cpus[n].props.cluster_id =
> >> +            n / (ms->smp.cores * ms->smp.threads);  
> > 
> > are there any relation cluster values here and number of clusters with
> > what virt_cpu_mp_affinity() calculates?
> >   
> 
> They're different clusters. The cluster returned by virt_cpu_mp_affinity()
> is reflected to MPIDR_EL1 system register, which is mainly used by VGIC2/3
> interrupt controller to send send group interrupts to the CPU cluster. It's
> notable that the value returned from virt_cpu_mp_affinity() is always
> overrided by KVM. It means this value is only used by TCG for the emulated
> GIC2/GIC3.
> 
> The cluster in 'ms->possible_cpus' is passed to ACPI PPTT table to populate
> the CPU topology.
> 
> 
> >> +        ms->possible_cpus->cpus[n].props.has_core_id = true;
> >> +        ms->possible_cpus->cpus[n].props.core_id = n / ms->smp.threads;  
> >   
> >>           ms->possible_cpus->cpus[n].props.has_thread_id = true;
> >>           ms->possible_cpus->cpus[n].props.thread_id = n;  
> > of cause target has the right to decide how to allocate IDs, and mgmt
> > is supposed to query these IDs before using them.
> > But:
> >   * IDs within 'props' are supposed to be arch defined.
> >     (on x86 IDs in range [0-smp.foo_id), on ppc it something different)
> >     Question is what real hardware does here in ARM case (i.e.
> >     how .../cores/threads are described on bare-metal)?
> >    
> 
> On ARM64 bare-metal machine, the core/cluster ID assignment is pretty 
> arbitrary.
> I checked the CPU topology on my bare-metal machine, which has following SMP
> configurations.
> 
>      # lscpu
>        :
>      Thread(s) per core: 4
>      Core(s) per socket: 28
>      Socket(s):          2
> 
>      smp.sockets  = 2
>      smp.clusters = 1
>      smp.cores    = 56   (28 per socket)
>      smp.threads  = 4
> 
>      // CPU0-111 belongs to socket0 or package0
>      // CPU112-223 belongs to socket1 or package1
>      # cat /sys/devices/system/cpu/cpu0/topology/package_cpus
>      00000000,00000000,00000000,0000ffff,ffffffff,ffffffff,ffffffff
>      # cat /sys/devices/system/cpu/cpu111/topology/package_cpus
>      00000000,00000000,00000000,0000ffff,ffffffff,ffffffff,ffffffff
>      # cat /sys/devices/system/cpu/cpu112/topology/package_cpus
>      ffffffff,ffffffff,ffffffff,ffff0000,00000000,00000000,00000000
>      # cat /sys/devices/system/cpu/cpu223/topology/package_cpus
>      ffffffff,ffffffff,ffffffff,ffff0000,00000000,00000000,00000000
> 
>      // core/cluster ID spans from 0 to 27 on socket0
>      # for i in `seq 0 27`; do cat 
> /sys/devices/system/cpu/cpu$i/topology/core_id; done
>      0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
>      # for i in `seq 28 55`; do cat 
> /sys/devices/system/cpu/cpu$i/topology/core_id; done
>      0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
>      # for i in `seq 0 27`; do cat 
> /sys/devices/system/cpu/cpu$i/topology/cluster_id; done
>      0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
>      # for i in `seq 28 55`; do cat 
> /sys/devices/system/cpu/cpu$i/topology/cluster_id; done
>      0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
>      
>      // However, core/cluster ID starts from 256 on socket1
>      # for i in `seq 112 139`; do cat 
> /sys/devices/system/cpu/cpu$i/topology/core_id; done
>      256 257 258 259 260 261 262 263 264 265 266 267 268 269
>      270 271 272 273 274 275 276 277 278 279 280 281 282 283
>      # for i in `seq 140 167`; do cat 
> /sys/devices/system/cpu/cpu$i/topology/core_id; done
>      256 257 258 259 260 261 262 263 264 265 266 267 268 269
>      270 271 272 273 274 275 276 277 278 279 280 281 282 283
>      # for i in `seq 112 139`; do cat 
> /sys/devices/system/cpu/cpu$i/topology/cluster_id; done
>      256 257 258 259 260 261 262 263 264 265 266 267 268 269
>      270 271 272 273 274 275 276 277 278 279 280 281 282 283
>      # for i in `seq 140 167`; do cat 
> /sys/devices/system/cpu/cpu$i/topology/cluster_id; done
>      256 257 258 259 260 261 262 263 264 265 266 267 268 269
>      270 271 272 273 274 275 276 277 278 279 280 281 282 283

so it seems that IDs are repeatable within a socket.
If there no arch defined way or other objections it might be better
to stick to what x86 does for consistency reasons  (i.e. socket/die/
cluster/core/thread are in range [0..x) including thread-id being
in range [0..threads) ) instead of inventing arm/virt specific scheme.

>     
> >   * maybe related: looks like build_pptt() and build_madt() diverge on
> >     the meaning of 'ACPI Processor ID' and how it's generated.
> >     My understanding of 'ACPI Processor ID' is that it should match
> >     across all tables. So UIDs generated in build_pptt() look wrong to me.
> > 
> >   * maybe related: build_pptt() looks broken wrt core/thread where it
> >     may create at the same time a  leaf core with a leaf thread underneath 
> > it,
> >     is such description actually valid?
> >   
> 
> Yes, the UIDs in MADT/PPTT should match. I'm not sure if I missed anything 
> here.
> I don't see how the UID in MADT and PPTT table are diverged. In both 
> functions,
> 'thread_id' is taken as UID.
> 
> In build_pptt(), when the entries for the cores becomes leaf, nothing will be
> pushed into @list, @length becomes zero for the loop to create entries for
> the threads. In this case, we won't have any entries created for threads.
> 
> >   
> >>       }
> >> diff --git a/qapi/machine.json b/qapi/machine.json
> >> index 42fc68403d..99c945f258 100644
> >> --- a/qapi/machine.json
> >> +++ b/qapi/machine.json
> >> @@ -868,10 +868,11 @@
> >>   # @node-id: NUMA node ID the CPU belongs to
> >>   # @socket-id: socket number within node/board the CPU belongs to
> >>   # @die-id: die number within socket the CPU belongs to (since 4.1)
> >> -# @core-id: core number within die the CPU belongs to
> >> +# @cluster-id: cluster number within die the CPU belongs to
> >> +# @core-id: core number within cluster the CPU belongs to  
> > 
> > s:cluster:cluster/die:
> >   
> 
> Ok. I will amend it like below in next respin:
> 
>      # @core-id: core number within cluster/die the CPU belongs to
> 
> I'm not sure if we need make similar changes for 'cluster_id' like below?
> 
>     # @cluster-id: cluster number within die/socket the CPU belongs to
>                                           ^^^^^^^^^^

maybe postpone it till die is supported?

> 
> >>   # @thread-id: thread number within core the CPU belongs to
> >>   #
> >> -# Note: currently there are 5 properties that could be present
> >> +# Note: currently there are 6 properties that could be present
> >>   #       but management should be prepared to pass through other
> >>   #       properties with device_add command to allow for future
> >>   #       interface extension. This also requires the filed names to be 
> >> kept in
> >> @@ -883,6 +884,7 @@
> >>     'data': { '*node-id': 'int',
> >>               '*socket-id': 'int',
> >>               '*die-id': 'int',
> >> +            '*cluster-id': 'int',
> >>               '*core-id': 'int',
> >>               '*thread-id': 'int'
> >>     }  
> 
> Thanks,
> Gavin
>