Re: [Qemu-devel] [PATCH v3 07/19] pc: set APIC ID based on socket/core/thread ids if it's not been set yet

[Eduardo Habkost]

On Wed, Jul 13, 2016 at 06:24:17PM -0400, Bandan Das wrote:
> Igor Mammedov <address@hidden> writes:
> 
> > 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>
> > ---
> > v3:
> >  - use %u for printing topo ids
> > v2:
> >  - add validity checks for socket-id/core-id/thread-id values
> > ---
> >  hw/i386/pc.c | 44 +++++++++++++++++++++++++++++++++++++++++---
> >  1 file changed, 41 insertions(+), 3 deletions(-)
> >
> > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > index 24231ca..29da2d4 100644
> > --- a/hw/i386/pc.c
> > +++ b/hw/i386/pc.c
> > @@ -1763,14 +1763,52 @@ 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_slot(pcms, CPU(dev), &idx);
> >  
> > +    /* if APIC ID is not set, set it based on socket/core/thread 
> > properties */
> > +    if (cpu->apic_id == UNASSIGNED_APIC_ID) {
> > +        int max_socket = (max_cpus - 1) / smp_threads / smp_cores;
> > +
> > +        if (cpu->socket_id < 0) {
> > +            error_setg(errp, "CPU socket-id is not set");
> > +            return;
> > +        } else if (cpu->socket_id > max_socket) {
> > +            error_setg(errp, "Invalid CPU socket-id: %u must be in range 
> > 0:%u",
> > +                       cpu->socket_id, max_socket);
> > +            return;
> > +        }
> > +        if (cpu->core_id < 0) {
> > +            error_setg(errp, "CPU core-id is not set");
> > +            return;
> > +        } else if (cpu->core_id > (smp_cores - 1)) {
> > +            error_setg(errp, "Invalid CPU core-id: %u must be in range 
> > 0:%u",
> > +                       cpu->core_id, smp_cores - 1);
> > +            return;
> > +        }
> > +        if (cpu->thread_id < 0) {
> > +            error_setg(errp, "CPU thread-id is not set");
> > +            return;
> > +        } else if (cpu->thread_id > (smp_threads - 1)) {
> > +            error_setg(errp, "Invalid CPU thread-id: %u must be in range 
> > 0:%u",
> > +                       cpu->thread_id, smp_threads - 1);
> > +            return;
> > +        }
> 
> Just curoious, when any of these values < 0, the only other values that they
> can take is -1, right ?

No, the user might have set thread=-2 explicitly, and this is
where we validate the user-provided values.

> I am wondering why decided to do the check differently
> for in the preceeding patch.

Because on both cases we want thread_id <= -2 to generate an
error message. On patch 06/19, thread_id == -1 is one case where
the error message will be skipped (but thread_id == -2 will
generate an error). In this patch, all negative values should
generate an error.

> 
> Bandan
> > +        topo.pkg_id = cpu->socket_id;
> > +        topo.core_id = cpu->core_id;
> > +        topo.smt_id = cpu->thread_id;
> > +        cpu->apic_id = apicid_from_topo_ids(smp_cores, smp_threads, &topo);
> > +    }
> > +
> > +    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,
> > +        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);
> >          return;
> >      }

-- 
Eduardo