Re: [Qemu-devel] [PATCH v3 06/18] numa: mirror cpu to node mapping in MachineState::possible_cpus

[Eduardo Habkost]

On Wed, May 10, 2017 at 01:29:50PM +0200, Igor Mammedov wrote:
[...]
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 2482c63..420c8c4 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -389,6 +389,102 @@ HotpluggableCPUList 
> *machine_query_hotpluggable_cpus(MachineState *machine)
[...]
> +void machine_set_cpu_numa_node(MachineState *machine,
> +                               const CpuInstanceProperties *props, Error 
> **errp)
> +{
[...]
> +    /* force board to initialize possible_cpus if it hasn't been done yet */
> +    mc->possible_cpu_arch_ids(machine);
[...]
> diff --git a/numa.c b/numa.c
> index 7182481..7db5dde 100644
> --- a/numa.c
> +++ b/numa.c
> @@ -170,6 +170,7 @@ static void parse_numa_node(MachineState *ms, 
> NumaNodeOptions *node,
>          exit(1);
>      }
>      for (cpus = node->cpus; cpus; cpus = cpus->next) {
> +        CpuInstanceProperties props;
>          if (cpus->value >= max_cpus) {
>              error_setg(errp,
>                         "CPU index (%" PRIu16 ")"
> @@ -178,6 +179,10 @@ static void parse_numa_node(MachineState *ms, 
> NumaNodeOptions *node,
>              return;
>          }
>          bitmap_set(numa_info[nodenr].node_cpu, cpus->value, 1);
> +        props = mc->cpu_index_to_instance_props(ms, cpus->value);
> +        props.node_id = nodenr;
> +        props.has_node_id = true;
> +        machine_set_cpu_numa_node(ms, &props, &error_fatal);

This triggers a call to possible_cpu_arch_ids() before
nb_numa_nodes is set to the actual number of NUMA nodes in the
machine, breaking the "node_id = ... % nb_numa_nodes"
initialization logic in pc, virt, and spapr.

The initialization ordering between possible_cpus and NUMA data
structures looks very subtle and fragile.  I still don't see an
obvious way to untangle that.

I suggest moving the default-NUMA-mapping code to a separate
machine class method, instead of relying on
possible_cpu_arch_ids() to initialize node_id.

-- 
Eduardo