node: Add heterogenous memory access attributes

Heterogeneous memory systems provide memory nodes with different latency
and bandwidth performance attributes. Provide a new kernel interface
for subsystems to register the attributes under the memory target
node's initiator access class. If the system provides this information,
applications may query these attributes when deciding which node to
request memory.

The following example shows the new sysfs hierarchy for a node exporting
performance attributes:

  # tree -P "read*|write*"/sys/devices/system/node/nodeY/accessZ/initiators/
  /sys/devices/system/node/nodeY/accessZ/initiators/
  |-- read_bandwidth
  |-- read_latency
  |-- write_bandwidth
  `-- write_latency

The bandwidth is exported as MB/s and latency is reported in
nanoseconds. The values are taken from the platform as reported by the
manufacturer.

Memory accesses from an initiator node that is not one of the memory's
access "Z" initiator nodes linked in the same directory may observe
different performance than reported here. When a subsystem makes use
of this interface, initiators of a different access number may not have
the same performance relative to initiators in other access numbers, or
omitted from the any access class' initiators.

Descriptions for memory access initiator performance access attributes
are added to sysfs stable documentation.

Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Tested-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, 26 insertions, 0 deletions

diff --git a/include/linux/node.h b/include/linux/node.h
index bb288817ed33..4139d728f8b3 100644
--- a/include/linux/node.h
+++ b/include/linux/node.h
@@ -20,6 +20,32 @@
 #include <linux/list.h>
 #include <linux/workqueue.h>
 
+/**
+ * struct node_hmem_attrs - heterogeneous memory performance attributes
+ *
+ * @read_bandwidth:	Read bandwidth in MB/s
+ * @write_bandwidth:	Write bandwidth in MB/s
+ * @read_latency:	Read latency in nanoseconds
+ * @write_latency:	Write latency in nanoseconds
+ */
+struct node_hmem_attrs {
+	unsigned int read_bandwidth;
+	unsigned int write_bandwidth;
+	unsigned int read_latency;
+	unsigned int write_latency;
+};
+
+#ifdef CONFIG_HMEM_REPORTING
+void node_set_perf_attrs(unsigned int nid, struct node_hmem_attrs *hmem_attrs,
+			 unsigned access);
+#else
+static inline void node_set_perf_attrs(unsigned int nid,
+				       struct node_hmem_attrs *hmem_attrs,
+				       unsigned access)
+{
+}
+#endif
+
 struct node {
 	struct device	dev;
 	struct list_head access_list;