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Re: [Qemu-devel] [PATCH 07/11] pc: set APIC ID based on socket/core/thre


From: Eduardo Habkost
Subject: Re: [Qemu-devel] [PATCH 07/11] pc: set APIC ID based on socket/core/thread ids if it's not been set yet
Date: Thu, 23 Jun 2016 16:27:46 -0300
User-agent: Mutt/1.6.1 (2016-04-27)

On Thu, Jun 23, 2016 at 07:48:24PM +0200, Igor Mammedov wrote:
> On Thu, 23 Jun 2016 14:19:16 -0300
> Eduardo Habkost <address@hidden> wrote:
> 
> > On Thu, Jun 23, 2016 at 04:54:25PM +0200, Igor Mammedov wrote:
> > > CPU added with device_add help won't have APIC ID set,
> > > so set it according to socket/core/thread ids provided
> > > with device_add command.
> > > 
> > > Signed-off-by: Igor Mammedov <address@hidden>
> > > ---
> > >  hw/i386/pc.c | 18 +++++++++++++-----
> > >  1 file changed, 13 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > > index 87352ae..63e9bb6 100644
> > > --- a/hw/i386/pc.c
> > > +++ b/hw/i386/pc.c
> > > @@ -1758,13 +1758,23 @@ static void pc_cpu_pre_plug(HotplugHandler
> > > *hotplug_dev, DeviceState *dev, Error **errp)
> > >  {
> > >      int idx;
> > > +    CPUArchId *cpu_slot;
> > > +    X86CPUTopoInfo topo;
> > >      X86CPU *cpu = X86_CPU(dev);
> > >      PCMachineState *pcms = PC_MACHINE(hotplug_dev);
> > > -    CPUArchId *cpu_slot = pc_find_cpu(pcms, CPU(dev), &idx);
> > >  
> > > +    if (cpu->apic_id == 0xFFFFFFFF) {
> > > +        /* APIC ID not set, set it based on socket/core/thread
> > > properties */
> > > +        X86CPUTopoInfo topo = { cpu->socket, cpu->core,
> > > cpu->thread };
> > > +        cpu->apic_id = apicid_from_topo_ids(smp_cores,
> > > smp_threads, &topo);
> > > +    }
> > 
> > What happens if neither apic-id or socket/core/thread are set?
> > 
> > apicid_from_topo_ids() needs the caller to ensure
> > core_id < nr_cores && smt_id < nr_threads. Do you do that?
> it will get wrong apic_id and error in "if (!cpu_slot)" will trigger,
> I can explicitly check for unset values report error saying that
> they must be set if you prefer.

Will it? If smp_cores=2 and smp_threads=2,
socket=0,core=0,thread=3 will generate a valid APIC ID
(corresponding to socket=0,core=1,thread=1).

About unset/invalid values: apicid_from_topo_ids() documentation
explicitly requires core_id < nr_cores && smt_id < nr_threads,
and may generate a valid APIC ID if only some of the
socket/core/thread values are set to -1.

(Also, if you don't check for missing/invalid values explicitly
you will generate a very confusing error message for the user).

> 
> > 
> > > +
> > > +    cpu_slot = pc_find_cpu(pcms, CPU(dev), &idx);
> > >      if (!cpu_slot) {
> > > -        error_setg(errp, "Invalid CPU index with APIC ID (%" PRIu32
> > > -                   "), valid range 0:%d", cpu->apic_id,
> > > +        x86_topo_ids_from_apicid(cpu->apic_id, smp_cores,
> > > smp_threads, &topo);
> > > +        error_setg(errp, "Invalid CPU[socket: %d, core: %d,
> > > thread: %d] with"
> > > +                  " APIC ID (%" PRIu32 "), valid index range 0:%d",
> > > +                   topo.pkg_id, topo.core_id, topo.smt_id,
> > > cpu->apic_id, pcms->possible_cpus->len - 1);
> > 
> > The error message is a bit confusing: the interface is not based
> > on CPU index anymore, but it still says "valid index range 0:%d".
> it's still based on CPU index for cpu-add and -numa cpus,
> so until we get rid of index in there it still should be printed.

OK.

> 
> > 
> > >          return;
> > >      }
> > > @@ -1780,8 +1790,6 @@ static void pc_cpu_pre_plug(HotplugHandler
> > > *hotplug_dev,
> > >       * added CPUs so that query_hotpluggable_cpus would show
> > > correct values */
> > >      if (cpu->thread == -1 || cpu->core == -1 || cpu->socket == -1)
> > > {
> > > -        X86CPUTopoInfo topo;
> > > -
> > >          x86_topo_ids_from_apicid(cpu->apic_id, smp_cores,
> > > smp_threads, &topo); cpu->thread = topo.smt_id;
> > >          cpu->core = topo.core_id;
> > > -- 
> > > 1.8.3.1
> > > 
> > 
> 

-- 
Eduardo



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