Re: [Qemu-devel] [PATCH 2/9] machine: introduce MachineClass.possible_cpu_arch_ids() hook

[Igor Mammedov]

On Fri, 5 Feb 2016 13:04:26 -0200
Eduardo Habkost <address@hidden> wrote:

> On Thu, Feb 04, 2016 at 12:47:28PM +0100, 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 figure out
> > what IDs are correct on its own.
> > 
> > Signed-off-by: Igor Mammedov <address@hidden>
> > ---
> >  hw/i386/pc.c        | 16 ++++++++++++++++
> >  include/hw/boards.h | 18 ++++++++++++++++++
> >  2 files changed, 34 insertions(+)
> > 
> > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > index d72246d..2fd8fc8 100644
> > --- a/hw/i386/pc.c
> > +++ b/hw/i386/pc.c
> > @@ -1946,6 +1946,21 @@ static unsigned pc_cpu_index_to_socket_id(unsigned 
> > cpu_index)
> >      return topo.pkg_id;
> >  }
> >  
> > +static GArray *pc_possible_cpu_arch_ids(void)
> > +{
> > +    int i;
> > +    GArray *list = g_array_new (FALSE, FALSE, sizeof (CPUArchId));
> > +
> > +    for (i = 0; i < max_cpus; i++) {
> > +        CPUArchId val;
> > +
> > +        val.arch_id = x86_cpu_apic_id_from_index(i);
> > +        val.cpu = qemu_get_cpu_by_arch_id(val.arch_id);
> > +        g_array_append_val(list, val);  
> 
> What about letting callers call qemu_get_cpu_by_arch_id() only if
> they really need it?
> 
> If you do that, you just need to return an uint64_t array, and
> there's no need for struct CPUArchId.
So far all callers that would use it would need to call
qemu_get_cpu_by_arch_id() so doing it in one place (here)
seems better than to duplicating that call over the code.

> 
> > +    }
> > +    return list;
> > +}  
> [...]
>