x86: use x2apic when supported on AMD

For core and package ids, x2apic scales to many more threads
than topoext. Hence AMD uses x2apic when available.

When x2apic isn't supported (up to Gen1 EPYC),
or when NUMA nodes are needed (disabled by default),
topoext is still useful.

Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>

hwloc/topology-x86.c

@@ -674,16 +674,20 @@ static void look_proc(struct hwloc_backend *backend, struct procinfo *infos, uns
    * Get the hierarchy of thread, core, die, package, etc. from CPU-specific leaves
    */
 
-  if (cpuid_type != intel && cpuid_type != zhaoxin && highest_ext_cpuid >= 0x80000008) {
+  if (cpuid_type != intel && cpuid_type != zhaoxin && highest_ext_cpuid >= 0x80000008 && !has_x2apic(features)) {
     /* Get core/thread information from cpuid 0x80000008
      * (not supported on Intel)
+     * We could ignore this codepath when x2apic is supported, but we may need
+     * nodeids if HWLOC_X86_TOPOEXT_NUMANODES is set.
      */
     read_amd_cores_legacy(infos, src_cpuiddump);
   }
 
   if (cpuid_type != intel && cpuid_type != zhaoxin && has_topoext(features)) {
     /* Get apicid, nodeid, unitid/coreid from cpuid 0x8000001e (AMD topology extension).
      * Requires read_amd_cores_legacy() for coreid on family 0x15-16.
+     *
+     * Only needed when x2apic supported if NUMA nodes are needed.
      */
     read_amd_cores_topoext(infos, src_cpuiddump);
   }
@@ -694,7 +698,8 @@ static void look_proc(struct hwloc_backend *backend, struct procinfo *infos, uns
      */
     read_intel_cores_exttopoenum(infos, 0x1f, src_cpuiddump);
 
-  } else if ((cpuid_type == intel || cpuid_type == zhaoxin) && highest_cpuid >= 0x0b && has_x2apic(features)) {
+  } else if ((cpuid_type == intel || cpuid_type == amd || cpuid_type == zhaoxin)
+	     && highest_cpuid >= 0x0b && has_x2apic(features)) {
     /* Get package/core/thread information from cpuid 0x0b
      * (Intel v1 Extended Topology Enumeration)
      */