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

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 13 Jul 2016 18:16:59 -0400
Bandan Das <bsd@redhat.com> wrote:

> 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.
This patch is called for every device,
so no there shouldn't be else error path here.

> 
> 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;
> >  }  
>