Re: [Qemu-devel] [PATCH v3 04/19] pc: cpu: consolidate apic-id validity checks in pc_cpu_pre_plug()

[Bandan Das <bsd@redhat.com>]

Igor Mammedov <imammedo@redhat.com> writes:

> Machine code knows about all possible APIC IDs so use that
> instead of hack which does O(n^2) complexity duplicate
> checks, interating over global CPUs list.
> As result duplicate check is done only once with O(log n) complexity.
>
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
>  hw/i386/pc.c      | 44 ++++++++++++++++++++++++++++++++------------
>  target-i386/cpu.c | 13 -------------
>  2 files changed, 32 insertions(+), 25 deletions(-)
>
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 3c42d84..99dfbe0 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1071,18 +1071,6 @@ void pc_hot_add_cpu(const int64_t id, Error **errp)
>          return;
>      }
>  
> -    if (cpu_exists(apic_id)) {
> -        error_setg(errp, "Unable to add CPU: %" PRIi64
> -                   ", it already exists", id);
> -        return;
> -    }
> -
> -    if (id >= max_cpus) {
> -        error_setg(errp, "Unable to add CPU: %" PRIi64
> -                   ", max allowed: %d", id, max_cpus - 1);
> -        return;
> -    }
> -
>      if (apic_id >= ACPI_CPU_HOTPLUG_ID_LIMIT) {
>          error_setg(errp, "Unable to add CPU: %" PRIi64
>                     ", resulting APIC ID (%" PRIi64 ") is too large",
> @@ -1771,6 +1759,37 @@ static void pc_cpu_unplug_cb(HotplugHandler *hotplug_dev,
>      error_propagate(errp, local_err);
>  }
>  
> +static void pc_cpu_pre_plug(HotplugHandler *hotplug_dev,
> +                            DeviceState *dev, Error **errp)
> +{
> +    int idx;
> +    X86CPU *cpu = X86_CPU(dev);
> +    PCMachineState *pcms = PC_MACHINE(hotplug_dev);
> +    CPUArchId *cpu_slot = pc_find_cpu_slot(pcms, CPU(dev), &idx);
> +
> +    if (!cpu_slot) {
> +        error_setg(errp, "Invalid CPU index with APIC ID (%" PRIu32
> +                   "), valid range 0:%d", cpu->apic_id,
> +                   pcms->possible_cpus->len - 1);
> +        return;
> +    }
> +
> +    if (cpu_slot->cpu) {
> +        error_setg(errp, "CPU[%ld] with APIC ID %" PRIu32 " exists",
> +                   cpu_slot - pcms->possible_cpus->cpus,
> +                   cpu->apic_id);
> +        return;
> +    }
> +}
> +
> +static void pc_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
> +                                          DeviceState *dev, Error **errp)
> +{
> +    if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
> +        pc_cpu_pre_plug(hotplug_dev, dev, errp);
> +    }
> +}
>

Will this path be invoked for non TYPE_CPU callbacks too ? I was just wondering
if there should be an "else" error message.

Bandan

>  static void pc_machine_device_plug_cb(HotplugHandler *hotplug_dev,
>                                        DeviceState *dev, Error **errp)
>  {
> @@ -2068,6 +2087,7 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
>      mc->hot_add_cpu = pc_hot_add_cpu;
>      mc->max_cpus = 255;
>      mc->reset = pc_machine_reset;
> +    hc->pre_plug = pc_machine_device_pre_plug_cb;
>      hc->plug = pc_machine_device_plug_cb;
>      hc->unplug_request = pc_machine_device_unplug_request_cb;
>      hc->unplug = pc_machine_device_unplug_cb;
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index e7319e3..9511474 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -1838,8 +1838,6 @@ static void x86_cpuid_set_apic_id(Object *obj, Visitor *v, const char *name,
>  {
>      X86CPU *cpu = X86_CPU(obj);
>      DeviceState *dev = DEVICE(obj);
> -    const int64_t min = 0;
> -    const int64_t max = UINT32_MAX;
>      Error *error = NULL;
>      int64_t value;
>  
> @@ -1854,17 +1852,6 @@ static void x86_cpuid_set_apic_id(Object *obj, Visitor *v, const char *name,
>          error_propagate(errp, error);
>          return;
>      }
> -    if (value < min || value > max) {
> -        error_setg(errp, "Property %s.%s doesn't take value %" PRId64
> -                   " (minimum: %" PRId64 ", maximum: %" PRId64 ")" ,
> -                   object_get_typename(obj), name, value, min, max);
> -        return;
> -    }
> -
> -    if ((value != cpu->apic_id) && cpu_exists(value)) {
> -        error_setg(errp, "CPU with APIC ID %" PRIi64 " exists", value);
> -        return;
> -    }
>      cpu->apic_id = value;
>  }