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

[Igor Mammedov]

On Thu, 3 Mar 2016 13:27:27 +0200
Marcel Apfelbaum <address@hidden> wrote:

> 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 <address@hidden>
> > ---
> >   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.
I'll fix it up to CPUArchId cpus[0]; and post fixed up path v5
as reply to this patch.

Thanks,
Igor

> 
> 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;
> >  
>