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

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 4 Feb 2016 14:18:10 +0200
Marcel Apfelbaum <marcel.apfelbaum@gmail.com> wrote:

> 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.
Then it wouldn't get CPU present status as there is no CPUs at that time.
It would also require refatoring of vl.c as machine_init() happens
before -smp is parsed.

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