node: Link memory nodes to their compute nodes

Systems may be constructed with various specialized nodes. Some nodes
may provide memory, some provide compute devices that access and use
that memory, and others may provide both. Nodes that provide memory are
referred to as memory targets, and nodes that can initiate memory access
are referred to as memory initiators.

Memory targets will often have varying access characteristics from
different initiators, and platforms may have ways to express those
relationships. In preparation for these systems, provide interfaces for
the kernel to export the memory relationship among different nodes memory
targets and their initiators with symlinks to each other.

If a system provides access locality for each initiator-target pair, nodes
may be grouped into ranked access classes relative to other nodes. The
new interface allows a subsystem to register relationships of varying
classes if available and desired to be exported.

A memory initiator may have multiple memory targets in the same access
class. The target memory's initiators in a given class indicate the
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.

A memory target node may have multiple memory initiators. All linked
initiators in a target's class have the same access characteristics to
that target.

The following example show the nodes' new sysfs hierarchy for a memory
target node 'Y' with access class 0 from initiator node 'X':

  # symlinks -v /sys/devices/system/node/nodeX/access0/
  relative: /sys/devices/system/node/nodeX/access0/targets/nodeY -> ../../nodeY

  # symlinks -v /sys/devices/system/node/nodeY/access0/
  relative: /sys/devices/system/node/nodeY/access0/initiators/nodeX -> ../../nodeX

The new attributes are added to the sysfs stable documentation.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Brice Goglin <Brice.Goglin@inria.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 24 insertions, 1 deletions

diff --git a/Documentation/ABI/stable/sysfs-devices-node b/Documentation/ABI/stable/sysfs-devices-node
index 3e90e1f3bf0a..433bcc04e542 100644
--- a/Documentation/ABI/stable/sysfs-devices-node
+++ b/Documentation/ABI/stable/sysfs-devices-node
@@ -90,4 +90,27 @@ Date:		December 2009
 Contact:	Lee Schermerhorn <lee.schermerhorn@hp.com>
 Description:
 		The node's huge page size control/query attributes.
-		See Documentation/admin-guide/mm/hugetlbpage.rst
\ No newline at end of file
+		See Documentation/admin-guide/mm/hugetlbpage.rst
+
+What:		/sys/devices/system/node/nodeX/accessY/
+Date:		December 2018
+Contact:	Keith Busch <keith.busch@intel.com>
+Description:
+		The node's relationship to other nodes for access class "Y".
+
+What:		/sys/devices/system/node/nodeX/accessY/initiators/
+Date:		December 2018
+Contact:	Keith Busch <keith.busch@intel.com>
+Description:
+		The directory containing symlinks to memory initiator
+		nodes that have class "Y" access to this target node's
+		memory. CPUs and other memory initiators in nodes not in
+		the list accessing this node's memory may have different
+		performance.
+
+What:		/sys/devices/system/node/nodeX/accessY/targets/
+Date:		December 2018
+Contact:	Keith Busch <keith.busch@intel.com>
+Description:
+		The directory containing symlinks to memory targets that
+		this initiator node has class "Y" access.