Re: [Qemu-devel] [PATCH v4 03/10] machine: introduce MachineClass.possible_cpu_arch_ids() hook

[Marcel Apfelbaum <marcel@redhat.com>]

On 02/26/2016 03:59 PM, Igor Mammedov wrote:
> on x86 currently range 0..max_cpus is used to generate
> architecture-dependent CPU ID (APIC Id) for each present
> and possible CPUs. However architecture-dependent CPU IDs
> list could be sparse and code that needs to enumerate
> all IDs (ACPI) ended up doing guess work enumerating all
> possible and impossible IDs up to
>    apic_id_limit = x86_cpu_apic_id_from_index(max_cpus).
>
> That leads to creation of MADT entries and Processor
> objects in ACPI tables for not possible CPUs.
> Fix it by allowing board specify a concrete list of
> CPU IDs accourding its own rules (which for x86 depends
> on topology). So that code that needs this list could
> request it from board instead of trying to guess
> what IDs are correct on its own.
>
> This interface will also allow to help making AML
> part of CPU hotplug target independent so it could
> be reused for ARM target.
>
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
>   hw/i386/pc.c         | 44 ++++++++++++++++++++++++++++++++++++++++----
>   include/hw/boards.h  | 26 ++++++++++++++++++++++++++
>   include/hw/i386/pc.h |  1 +
>   3 files changed, 67 insertions(+), 4 deletions(-)
>
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 151a64c..5ce9295 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1132,10 +1132,17 @@ void pc_cpus_init(PCMachineState *pcms)
>           exit(1);
>       }
>
> -    for (i = 0; i < smp_cpus; i++) {
> -        cpu = pc_new_cpu(machine->cpu_model, x86_cpu_apic_id_from_index(i),
> -                         &error_fatal);
> -        object_unref(OBJECT(cpu));
> +    pcms->possible_cpus = g_malloc0(sizeof(CPUArchIdList) +
> +                                    sizeof(CPUArchId) * (max_cpus - 1));
> +    for (i = 0; i < max_cpus; i++) {
> +        pcms->possible_cpus->cpus[i].arch_id = x86_cpu_apic_id_from_index(i);
> +        pcms->possible_cpus->len++;
> +        if (i < smp_cpus) {
> +            cpu = pc_new_cpu(machine->cpu_model, x86_cpu_apic_id_from_index(i),
> +                             &error_fatal);
> +            pcms->possible_cpus->cpus[i].cpu = CPU(cpu);
> +            object_unref(OBJECT(cpu));
> +        }
>       }
>
>       /* tell smbios about cpuid version and features */
> @@ -1658,9 +1665,19 @@ static void pc_dimm_unplug(HotplugHandler *hotplug_dev,
>       error_propagate(errp, local_err);
>   }
>
> +static int pc_apic_cmp(const void *a, const void *b)
> +{
> +   CPUArchId *apic_a = (CPUArchId *)a;
> +   CPUArchId *apic_b = (CPUArchId *)b;
> +
> +   return apic_a->arch_id - apic_b->arch_id;
> +}
> +
>   static void pc_cpu_plug(HotplugHandler *hotplug_dev,
>                           DeviceState *dev, Error **errp)
>   {
> +    CPUClass *cc = CPU_GET_CLASS(dev);
> +    CPUArchId apic_id, *found_cpu;
>       HotplugHandlerClass *hhc;
>       Error *local_err = NULL;
>       PCMachineState *pcms = PC_MACHINE(hotplug_dev);
> @@ -1683,6 +1700,13 @@ static void pc_cpu_plug(HotplugHandler *hotplug_dev,
>
>       /* increment the number of CPUs */
>       rtc_set_memory(pcms->rtc, 0x5f, rtc_get_memory(pcms->rtc, 0x5f) + 1);
> +
> +    apic_id.arch_id = cc->get_arch_id(CPU(dev));
> +    found_cpu = bsearch(&apic_id, pcms->possible_cpus->cpus,
> +        pcms->possible_cpus->len, sizeof(*pcms->possible_cpus->cpus),
> +        pc_apic_cmp);
> +    assert(found_cpu);
> +    found_cpu->cpu = CPU(dev);
>   out:
>       error_propagate(errp, local_err);
>   }
> @@ -1925,6 +1949,17 @@ static unsigned pc_cpu_index_to_socket_id(unsigned cpu_index)
>       return topo.pkg_id;
>   }
>
> +static CPUArchIdList *pc_possible_cpu_arch_ids(MachineState *machine)
> +{
> +    PCMachineState *pcms = PC_MACHINE(machine);
> +    int len = sizeof(CPUArchIdList) +
> +              sizeof(CPUArchId) * (pcms->possible_cpus->len - 1);
> +    CPUArchIdList *list = g_malloc(len);
> +
> +    memcpy(list, pcms->possible_cpus, len);
> +    return list;
> +}
> +
>   static void pc_machine_class_init(ObjectClass *oc, void *data)
>   {
>       MachineClass *mc = MACHINE_CLASS(oc);
> @@ -1947,6 +1982,7 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
>       pcmc->save_tsc_khz = true;
>       mc->get_hotplug_handler = pc_get_hotpug_handler;
>       mc->cpu_index_to_socket_id = pc_cpu_index_to_socket_id;
> +    mc->possible_cpu_arch_ids = pc_possible_cpu_arch_ids;
>       mc->default_boot_order = "cad";
>       mc->hot_add_cpu = pc_hot_add_cpu;
>       mc->max_cpus = 255;
> diff --git a/include/hw/boards.h b/include/hw/boards.h
> index de3b3bd..c9b11d4 100644
> --- a/include/hw/boards.h
> +++ b/include/hw/boards.h
> @@ -8,6 +8,7 @@
>   #include "sysemu/accel.h"
>   #include "hw/qdev.h"
>   #include "qom/object.h"
> +#include "qom/cpu.h"
>
>   void memory_region_allocate_system_memory(MemoryRegion *mr, Object *owner,
>                                             const char *name,
> @@ -42,6 +43,26 @@ bool machine_dump_guest_core(MachineState *machine);
>   bool machine_mem_merge(MachineState *machine);
>
>   /**
> + * CPUArchId:
> + * @arch_id - architecture-dependent CPU ID of present or possible CPU
> + * @cpu - pointer to corresponding CPU object if it's present on NULL otherwise
> + */
> +typedef struct {
> +    uint64_t arch_id;
> +    struct CPUState *cpu;
> +} CPUArchId;
> +
> +/**
> + * CPUArchIdList:
> + * @len - number of @CPUArchId items in @cpus array
> + * @cpus - array of present or possible CPUs for current machine configuration
> + */
> +typedef struct {
> +    int len;
> +    CPUArchId cpus[1];

Hi Igor,

The patch looks good to me,
I just have one question. Why do you have cpus[1] in CPUArchIdList and not cpus[0]?

I suppose is to say that every machine has at least one cpu..., on the other
hand that leads to "not standard" usage like when allocating cpus you need a "-1" and so on.

Thanks,
Marcel



> +} CPUArchIdList;
> +
> +/**
>    * MachineClass:
>    * @get_hotplug_handler: this function is called during bus-less
>    *    device hotplug. If defined it returns pointer to an instance
> @@ -57,6 +78,10 @@ bool machine_mem_merge(MachineState *machine);
>    *    Set only by old machines because they need to keep
>    *    compatibility on code that exposed QEMU_VERSION to guests in
>    *    the past (and now use qemu_hw_version()).
> + * @possible_cpu_arch_ids:
> + *    Returns an array of @CPUArchId architecture-dependent CPU IDs
> + *    which includes CPU IDs for present and possible to hotplug CPUs.
> + *    Caller is responsible for freeing returned list.
>    */
>   struct MachineClass {
>       /*< private >*/
> @@ -98,6 +123,7 @@ struct MachineClass {
>       HotplugHandler *(*get_hotplug_handler)(MachineState *machine,
>                                              DeviceState *dev);
>       unsigned (*cpu_index_to_socket_id)(unsigned cpu_index);
> +    CPUArchIdList *(*possible_cpu_arch_ids)(MachineState *machine);
>   };
>
>   /**
> diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> index 8b3546e..3e09232 100644
> --- a/include/hw/i386/pc.h
> +++ b/include/hw/i386/pc.h
> @@ -65,6 +65,7 @@ struct PCMachineState {
>       /* CPU and apic information: */
>       bool apic_xrupt_override;
>       unsigned apic_id_limit;
> +    CPUArchIdList *possible_cpus;
>
>       /* NUMA information: */
>       uint64_t numa_nodes;
>