Re: [Qemu-devel] [PATCH 2/9] machine: introduce MachineClass.possible_cpu_arch_ids() hook

[Marcel Apfelbaum <marcel.apfelbaum@gmail.com>]

On 02/04/2016 01:47 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 figure out
> what IDs are correct on its own.
>
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
>   hw/i386/pc.c        | 16 ++++++++++++++++
>   include/hw/boards.h | 18 ++++++++++++++++++
>   2 files changed, 34 insertions(+)
>
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index d72246d..2fd8fc8 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1946,6 +1946,21 @@ static unsigned pc_cpu_index_to_socket_id(unsigned cpu_index)
>       return topo.pkg_id;
>   }
>
> +static GArray *pc_possible_cpu_arch_ids(void)
> +{
> +    int i;
> +    GArray *list = g_array_new (FALSE, FALSE, sizeof (CPUArchId));
> +
> +    for (i = 0; i < max_cpus; i++) {
> +        CPUArchId val;
> +
> +        val.arch_id = x86_cpu_apic_id_from_index(i);
> +        val.cpu = qemu_get_cpu_by_arch_id(val.arch_id);
> +        g_array_append_val(list, val);
> +    }
> +    return list;
> +}
> +
>   static void pc_machine_class_init(ObjectClass *oc, void *data)
>   {
>       MachineClass *mc = MACHINE_CLASS(oc);
> @@ -1968,6 +1983,7 @@ 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 0f30959..bd85f46 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 +43,16 @@ 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 ii it's present on NULL otherwise
> + */
> +typedef struct {
> +    uint64_t arch_id;
> +    struct CPUState *cpu;
> +} CPUArchId;
> +
> +/**
>    * MachineClass:
>    * @get_hotplug_handler: this function is called during bus-less
>    *    device hotplug. If defined it returns pointer to an instance
> @@ -57,6 +68,10 @@ 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 >*/
> @@ -99,8 +114,11 @@ struct MachineClass {
>       HotplugHandler *(*get_hotplug_handler)(MachineState *machine,
>                                              DeviceState *dev);
>       unsigned (*cpu_index_to_socket_id)(unsigned cpu_index);
> +    GArray *(*possible_cpu_arch_ids)(void);

Hi Igor,

Can't this be a GArray filled in at machine init time instead of a method?
Just wondering.

Thanks,
Marcel

>   };
>
> +#define FETCH_CPU_ARCH_ID(array, idx) g_array_index(array, CPUArchId, idx)
> +
>   /**
>    * MachineState:
>    */
>