Re: [Qemu-devel] [PATCH for-2.10 05/23] numa: move source of default CPUs to NUMA node mapping into boards

[Igor Mammedov <imammedo@redhat.com>]

On Tue, 28 Mar 2017 15:19:20 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Wed, Mar 22, 2017 at 02:32:30PM +0100, Igor Mammedov wrote:
[...]
answering to questions that I forgot to answer before

> > @@ -1554,6 +1554,16 @@ static void virt_set_gic_version(Object *obj, const char *value, Error **errp)
> >      }
> >  }
> >  
> > +static CpuInstanceProperties
> > +virt_cpu_index_to_props(MachineState *ms, unsigned cpu_index)
> > +{
> > +    MachineClass *mc = MACHINE_GET_CLASS(ms);
> > +    const CPUArchIdList *possible_cpus = mc->possible_cpu_arch_ids(ms);
> > +
> > +    assert(cpu_index < possible_cpus->len);
> > +    return possible_cpus->cpus[cpu_index].props;;
> > +}
> > +  
> 
> It seems a bit weird to have a machine specific hook to pull the
> property information when one way or another it's coming from the
> possible_cpus table, which is already constructed by a machine
> specific hook.  Could we add a range or list of cpu_index values to
> each possible_cpus entry instead, and have a generic lookup of the
> right entry based on that?
Mainly I dislike the idea because it adds duplicate data to manage
that could be computed from already stored there CpuInstanceProperties.

And secondly if it were just 1 number then generic lookup would be trivial
but with list it becomes cumbersome to manage and implementation
larger then 3 *_cpu_index_to_props() hooks combined, it's not worth it
in foreseeable future.
 
> >  static const CPUArchIdList *virt_possible_cpu_arch_ids(MachineState *ms)
> >  {
> >      int n;
> > @@ -1573,8 +1583,12 @@ static const CPUArchIdList *virt_possible_cpu_arch_ids(MachineState *ms)
> >          ms->possible_cpus->cpus[n].props.has_thread_id = true;
> >          ms->possible_cpus->cpus[n].props.thread_id = n;
> >  
> > -        /* TODO: add 'has_node/node' here to describe
> > -           to which node core belongs */
> > +        /* default distribution of CPUs over NUMA nodes */
> > +        if (nb_numa_nodes) {
> > +            /* preset values but do not enable them i.e. 'has_node_id = false',
> > +             * board will enable them if manual mapping wasn't present on CLI */  
> 
> I'm a little confused by this comment, since I don't see any board
> code altering has_node_id.
it happens in the last 2 hunks of patch 10/23
may be I should write it like this:

+            /* preset values but do not enable them i.e. 'has_node_id = false',
+             * numa initialization code will enable them later if manual mapping
+             * wasn't present on CLI */

> 
> > +            ms->possible_cpus->cpus[n].props.node_id = n % nb_numa_nodes;;
> > +        }
> >      }
> >      return ms->possible_cpus;
> >  }
[...]