On Wed, May 10, 2017 at 01:29:45PM +0200, Igor Mammedov wrote:
> Originally CPU threads were by default assigned in
> round-robin fashion. However it was causing issues in
> guest since CPU threads from the same socket/core could
> be placed on different NUMA nodes.
> Commit fb43b73b (pc: fix default VCPU to NUMA node mapping)
> fixed it by grouping threads within a socket on the same node
> introducing cpu_index_to_socket_id() callback and commit
> 20bb648d (spapr: Fix default NUMA node allocation for threads)
> reused callback to fix similar issues for SPAPR machine
> even though socket doesn't make much sense there.
> 
> As result QEMU ended up having 3 default distribution rules
> used by 3 targets /virt-arm, spapr, pc/.
> 
> In effort of moving NUMA mapping for CPUs into possible_cpus,
> generalize default mapping in numa.c by making boards decide
> on default mapping and let them explicitly tell generic
> numa code to which node a CPU thread belongs to by replacing
> cpu_index_to_socket_id() with @cpu_index_to_instance_props()
> which provides default node_id assigned by board to specified
> cpu_index.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

[snip]
> +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;
> +}

Suggested follow up patch: Since this function is identical for x86
and ARM, we could have a "thread_granularity_cpu_index_to_props"
helper they could both reference.  M

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson