Re: [PATCH v4 1/6] hw/loongarch/virt: Add CPU topology support

[Igor Mammedov <imammedo@redhat.com>]

On Tue, 12 Nov 2024 10:17:33 +0800
Bibo Mao <maobibo@loongson.cn> wrote:

> Add topological relationships for Loongarch VCPU and initialize
> topology member variables. Also physical cpu id calculation
> method comes from its topo information.
> 
> Co-developed-by: Xianglai Li <lixianglai@loongson.cn>
> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
> ---
>  docs/system/loongarch/virt.rst | 31 +++++++++++++++
>  hw/loongarch/virt.c            | 73 ++++++++++++++++++++++++++++------
>  target/loongarch/cpu.c         | 12 ++++++
>  target/loongarch/cpu.h         | 16 ++++++++
>  4 files changed, 119 insertions(+), 13 deletions(-)
> 
> diff --git a/docs/system/loongarch/virt.rst b/docs/system/loongarch/virt.rst
> index 172fba079e..8daf60785f 100644
> --- a/docs/system/loongarch/virt.rst
> +++ b/docs/system/loongarch/virt.rst
> @@ -28,6 +28,37 @@ The ``qemu-system-loongarch64`` provides emulation for virt
>  machine. You can specify the machine type ``virt`` and
>  cpu type ``la464``.
>  
> +CPU Topology
> +------------
> +
> +The ``LA464`` type CPUs have the concept of Socket Core and Thread.
> +
> +For example:
> +
> +``-smp 1,maxcpus=M,sockets=S,cores=C,threads=T``
> +
> +The above parameters indicate that the machine has a maximum of ``M`` vCPUs and
> +``S`` sockets, each socket has ``C`` cores, each core has ``T`` threads,
> +and each thread corresponds to a vCPU.
> +
> +Then ``M`` ``S`` ``C`` ``T`` has the following relationship:
> +
> +``M = S * C * T``
> +
> +In the CPU topology relationship, When we know the ``socket_id`` ``core_id``
> +and ``thread_id`` of the CPU, we can calculate its ``arch_id``:
> +
> +``arch_id = (socket_id * S) + (core_id * C) + (thread_id * T)``

Is there a spec or some other reference where all of this is described?
(or is that a made up just for QEMU?)


> +
> +Similarly, when we know the ``arch_id`` of the CPU,
> +we can also get its ``socket_id`` ``core_id`` and ``thread_id``:
> +
> +``socket_id = arch_id / (C * T)``
> +
> +``core_id = (arch_id / T) % C``
> +
> +``thread_id = arch_id % T``
> +
>  Boot options
>  ------------
>  
> diff --git a/hw/loongarch/virt.c b/hw/loongarch/virt.c
> index 9a635d1d3d..1ed5130edf 100644
> --- a/hw/loongarch/virt.c
> +++ b/hw/loongarch/virt.c
> @@ -1143,9 +1143,9 @@ static void virt_init(MachineState *machine)
>      LoongArchVirtMachineState *lvms = LOONGARCH_VIRT_MACHINE(machine);
>      int i;
>      hwaddr base, size, ram_size = machine->ram_size;
> -    const CPUArchIdList *possible_cpus;
>      MachineClass *mc = MACHINE_GET_CLASS(machine);
>      CPUState *cpu;
> +    Object *cpuobj;
>  
>      if (!cpu_model) {
>          cpu_model = LOONGARCH_CPU_TYPE_NAME("la464");
> @@ -1163,13 +1163,30 @@ static void virt_init(MachineState *machine)
>      memory_region_add_subregion(&lvms->system_iocsr, 0, &lvms->iocsr_mem);
>  
>      /* Init CPUs */
> -    possible_cpus = mc->possible_cpu_arch_ids(machine);
I'd keep this, and use below, it makes line shorter


> -    for (i = 0; i < possible_cpus->len; i++) {
> -        cpu = cpu_create(machine->cpu_type);
> +    mc->possible_cpu_arch_ids(machine);
> +    for (i = 0; i < machine->smp.cpus; i++) {
> +        cpuobj = object_new(machine->cpu_type);
> +        if (cpuobj == NULL) {
> +            error_report("Fail to create object with type %s ",
> +                         machine->cpu_type);
> +            exit(EXIT_FAILURE);
> +        }
> +
> +        cpu = CPU(cpuobj);

>          cpu->cpu_index = i;
this probably should be in _pre_plug handler,
also see
(a15d2728a9aa pc: Init CPUState->cpu_index with index in possible_cpus[])
for why x86 does it. 

>          machine->possible_cpus->cpus[i].cpu = cpu;
> -        lacpu = LOONGARCH_CPU(cpu);
> +        lacpu = LOONGARCH_CPU(cpuobj);

>          lacpu->phy_id = machine->possible_cpus->cpus[i].arch_id;
Given above is derived from topo data set below, I'd move above above
to pre_plug time, and calculate/set it there based on topo data.
There is no point in setting both at the same place. 

> +        object_property_set_int(cpuobj, "socket-id",
> +                                machine->possible_cpus->cpus[i].props.socket_id,
> +                                NULL);
> +        object_property_set_int(cpuobj, "core-id",
> +                                machine->possible_cpus->cpus[i].props.core_id,
> +                                NULL);
> +        object_property_set_int(cpuobj, "thread-id",
> +                                machine->possible_cpus->cpus[i].props.thread_id,
> +                                NULL);
> +        qdev_realize_and_unref(DEVICE(cpuobj), NULL, &error_fatal);
>      }
>      fdt_add_cpu_nodes(lvms);
>      fdt_add_memory_nodes(machine);
> @@ -1286,6 +1303,35 @@ static void virt_initfn(Object *obj)
>      virt_flash_create(lvms);
>  }
>  
> +static int virt_get_arch_id_from_topo(MachineState *ms, LoongArchCPUTopo *topo)
> +{
> +    int arch_id, sock_vcpu_num, core_vcpu_num;
> +
> +    /*
> +     * calculate total logical cpus across socket/core/thread.
> +     * For more information on how to calculate the arch_id,
> +     * you can refer to the CPU Topology chapter of the
> +     * docs/system/loongarch/virt.rst document.
> +     */
> +    sock_vcpu_num = topo->socket_id * (ms->smp.threads * ms->smp.cores);
> +    core_vcpu_num = topo->core_id * ms->smp.threads;
> +
> +    /* get vcpu-id(logical cpu index) for this vcpu from this topology */
> +    arch_id = (sock_vcpu_num + core_vcpu_num) + topo->thread_id;
> +
> +    assert(arch_id >= 0 && arch_id < ms->possible_cpus->len);
> +
> +    return arch_id;
> +}
> +
> +static void virt_get_topo_from_index(MachineState *ms,
> +                                     LoongArchCPUTopo *topo, int index)
> +{
> +    topo->socket_id = index / (ms->smp.cores * ms->smp.threads);
> +    topo->core_id = index / ms->smp.threads % ms->smp.cores;
> +    topo->thread_id = index % ms->smp.threads;
> +}
> +
>  static bool memhp_type_supported(DeviceState *dev)
>  {
>      /* we only support pc dimm now */
> @@ -1385,8 +1431,9 @@ static HotplugHandler *virt_get_hotplug_handler(MachineState *machine,
>  
>  static const CPUArchIdList *virt_possible_cpu_arch_ids(MachineState *ms)
>  {
> -    int n;
> +    int n, arch_id;
>      unsigned int max_cpus = ms->smp.max_cpus;
> +    LoongArchCPUTopo topo;
>  
>      if (ms->possible_cpus) {
>          assert(ms->possible_cpus->len == max_cpus);
> @@ -1397,17 +1444,17 @@ static const CPUArchIdList *virt_possible_cpu_arch_ids(MachineState *ms)
>                                    sizeof(CPUArchId) * max_cpus);
>      ms->possible_cpus->len = max_cpus;
>      for (n = 0; n < ms->possible_cpus->len; n++) {
> +        virt_get_topo_from_index(ms, &topo, n);
> +        arch_id = virt_get_arch_id_from_topo(ms, &topo);
> +        ms->possible_cpus->cpus[n].vcpus_count = 1;
>          ms->possible_cpus->cpus[n].type = ms->cpu_type;
> -        ms->possible_cpus->cpus[n].arch_id = n;
> -
> +        ms->possible_cpus->cpus[n].arch_id = arch_id;
>          ms->possible_cpus->cpus[n].props.has_socket_id = true;
> -        ms->possible_cpus->cpus[n].props.socket_id  =
> -                                   n / (ms->smp.cores * ms->smp.threads);
> +        ms->possible_cpus->cpus[n].props.socket_id = topo.socket_id;
>          ms->possible_cpus->cpus[n].props.has_core_id = true;
> -        ms->possible_cpus->cpus[n].props.core_id =
> -                                   n / ms->smp.threads % ms->smp.cores;
> +        ms->possible_cpus->cpus[n].props.core_id = topo.core_id;
>          ms->possible_cpus->cpus[n].props.has_thread_id = true;
> -        ms->possible_cpus->cpus[n].props.thread_id = n % ms->smp.threads;
> +        ms->possible_cpus->cpus[n].props.thread_id = topo.thread_id;
>      }
>      return ms->possible_cpus;
>  }
> diff --git a/target/loongarch/cpu.c b/target/loongarch/cpu.c
> index 57cc4f314b..a99e22094e 100644
> --- a/target/loongarch/cpu.c
> +++ b/target/loongarch/cpu.c
> @@ -16,6 +16,7 @@
>  #include "kvm/kvm_loongarch.h"
>  #include "exec/exec-all.h"
>  #include "cpu.h"
> +#include "hw/qdev-properties.h"
>  #include "internals.h"
>  #include "fpu/softfloat-helpers.h"
>  #include "cpu-csr.h"
> @@ -725,6 +726,7 @@ static void loongarch_cpu_init(Object *obj)
>      timer_init_ns(&cpu->timer, QEMU_CLOCK_VIRTUAL,
>                    &loongarch_constant_timer_cb, cpu);
>  #endif
> +    cpu->phy_id = UNSET_PHY_ID;
>  #endif
>  }
>  
> @@ -823,6 +825,14 @@ static int64_t loongarch_cpu_get_arch_id(CPUState *cs)
>  }
>  #endif
>  
> +static Property loongarch_cpu_properties[] = {
> +    DEFINE_PROP_INT32("socket-id", LoongArchCPU, socket_id, 0),
> +    DEFINE_PROP_INT32("core-id", LoongArchCPU, core_id, 0),
> +    DEFINE_PROP_INT32("thread-id", LoongArchCPU, thread_id, 0),
> +    DEFINE_PROP_INT32("node-id", LoongArchCPU, node_id, CPU_UNSET_NUMA_NODE_ID),
> +    DEFINE_PROP_END_OF_LIST()
> +};
> +
>  static void loongarch_cpu_class_init(ObjectClass *c, void *data)
>  {
>      LoongArchCPUClass *lacc = LOONGARCH_CPU_CLASS(c);
> @@ -830,6 +840,7 @@ static void loongarch_cpu_class_init(ObjectClass *c, void *data)
>      DeviceClass *dc = DEVICE_CLASS(c);
>      ResettableClass *rc = RESETTABLE_CLASS(c);
>  
> +    device_class_set_props(dc, loongarch_cpu_properties);
>      device_class_set_parent_realize(dc, loongarch_cpu_realizefn,
>                                      &lacc->parent_realize);
>      resettable_class_set_parent_phases(rc, NULL, loongarch_cpu_reset_hold, NULL,
> @@ -854,6 +865,7 @@ static void loongarch_cpu_class_init(ObjectClass *c, void *data)
>  #ifdef CONFIG_TCG
>      cc->tcg_ops = &loongarch_tcg_ops;
>  #endif
> +    dc->user_creatable = true;
>  }
>  
>  static const gchar *loongarch32_gdb_arch_name(CPUState *cs)
> diff --git a/target/loongarch/cpu.h b/target/loongarch/cpu.h
> index 86c86c6c95..7472df0521 100644
> --- a/target/loongarch/cpu.h
> +++ b/target/loongarch/cpu.h
> @@ -19,6 +19,12 @@
>  #include "cpu-csr.h"
>  #include "cpu-qom.h"
>  
> +/*
> + * CPU can't have 0xFFFFFFFF physical ID, use that value to distinguish
> + * that physical ID hasn't been set yet

pointer to CPU spec/doc here would be nice to have

> + */
> +#define UNSET_PHY_ID 0xFFFFFFFF
> +
>  #define IOCSRF_TEMP             0
>  #define IOCSRF_NODECNT          1
>  #define IOCSRF_MSI              2
> @@ -390,6 +396,12 @@ typedef struct CPUArchState {
>  #endif
>  } CPULoongArchState;
>  
> +typedef struct LoongArchCPUTopo {
> +    int32_t socket_id;  /* socket-id of this VCPU */
> +    int32_t core_id;    /* core-id of this VCPU */
> +    int32_t thread_id;  /* thread-id of this VCPU */
> +} LoongArchCPUTopo;
> +
>  /**
>   * LoongArchCPU:
>   * @env: #CPULoongArchState
> @@ -404,6 +416,10 @@ struct ArchCPU {
>      uint32_t  phy_id;
>      OnOffAuto lbt;
>      OnOffAuto pmu;
> +    int32_t socket_id;  /* socket-id of this VCPU */
> +    int32_t core_id;    /* core-id of this VCPU */
> +    int32_t thread_id;  /* thread-id of this VCPU */
> +    int32_t node_id;    /* NUMA node of this VCPU */
>  
>      /* 'compatible' string for this CPU for Linux device trees */
>      const char *dtb_compatible;