docs: mm: numaperf.rst Add brief description for access class 1.

Try to make minimal changes to the document which already describes
access class 0 in a generic fashion (including IO initiatiors that
are not CPUs).

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/admin-guide/mm/numaperf.rst

@@ -56,6 +56,11 @@ nodes' access characteristics share the same performance relative to other
 linked initiator nodes. Each target within an initiator's access class,
 though, do not necessarily perform the same as each other.
 
+The access class "1" is used to allow differentiation between initiators
+that are CPUs and hence suitable for generic task scheduling, and
+IO initiators such as GPUs and NICs.  Unlike access class 0, only
+nodes containing CPUs are considered.
+
 ================
 NUMA Performance
 ================
@@ -88,6 +93,9 @@ The latency attributes are provided in nanoseconds.
 The values reported here correspond to the rated latency and bandwidth
 for the platform.
 
+Access class 1 takes the same form but only includes values for CPU to
+memory activity.
+
 ==========
 NUMA Cache
 ==========