cxl/region: Support to calculate memory tier abstract distance

An abstract distance value must be assigned by the driver that makes
the memory available to the system. It reflects relative performance
and is used to place memory nodes backed by CXL regions in the appropriate
memory tiers allowing promotion/demotion within the existing memory tiering
mechanism.

The abstract distance is calculated based on the memory access latency
and bandwidth of CXL regions.
Signed-off-by: Huang, Ying <ying.huang@intel.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Cc: Alison Schofield <alison.schofield@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Bharata B Rao <bharata@amd.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://patch.msgid.link/20240618084639.1419629-3-ying.huang@intel.comSigned-off-by: Dave Jiang <dave.jiang@intel.com>

drivers/cxl/core/region.c

@@ -9,6 +9,7 @@
 #include <linux/uuid.h>
 #include <linux/sort.h>
 #include <linux/idr.h>
+#include <linux/memory-tiers.h>
 #include <cxlmem.h>
 #include <cxl.h>
 #include "core.h"
@@ -2228,6 +2229,7 @@ static void unregister_region(void *_cxlr)
 	int i;
 
 	unregister_memory_notifier(&cxlr->memory_notifier);
+	unregister_mt_adistance_algorithm(&cxlr->adist_notifier);
 	device_del(&cxlr->dev);
 
 	/*
@@ -2340,6 +2342,27 @@ static int cxl_region_perf_attrs_callback(struct notifier_block *nb,
 	return NOTIFY_OK;
 }
 
+static int cxl_region_calculate_adistance(struct notifier_block *nb,
+					  unsigned long nid, void *data)
+{
+	struct cxl_region *cxlr = container_of(nb, struct cxl_region,
+					       adist_notifier);
+	struct access_coordinate *perf;
+	int *adist = data;
+	int region_nid;
+
+	region_nid = cxl_region_nid(cxlr);
+	if (nid != region_nid)
+		return NOTIFY_OK;
+
+	perf = &cxlr->coord[ACCESS_COORDINATE_CPU];
+
+	if (mt_perf_to_adistance(perf, adist))
+		return NOTIFY_OK;
+
+	return NOTIFY_STOP;
+}
+
 /**
  * devm_cxl_add_region - Adds a region to a decoder
  * @cxlrd: root decoder
@@ -2382,6 +2405,10 @@ static struct cxl_region *devm_cxl_add_region(struct cxl_root_decoder *cxlrd,
 	cxlr->memory_notifier.priority = CXL_CALLBACK_PRI;
 	register_memory_notifier(&cxlr->memory_notifier);
 
+	cxlr->adist_notifier.notifier_call = cxl_region_calculate_adistance;
+	cxlr->adist_notifier.priority = 100;
+	register_mt_adistance_algorithm(&cxlr->adist_notifier);
+
 	rc = devm_add_action_or_reset(port->uport_dev, unregister_region, cxlr);
 	if (rc)
 		return ERR_PTR(rc);

drivers/cxl/cxl.h

@@ -522,6 +522,7 @@ struct cxl_region_params {
  * @params: active + config params for the region
  * @coord: QoS access coordinates for the region
  * @memory_notifier: notifier for setting the access coordinates to node
+ * @adist_notifier: notifier for calculating the abstract distance of node
  */
 struct cxl_region {
 	struct device dev;
@@ -534,6 +535,7 @@ struct cxl_region {
 	struct cxl_region_params params;
 	struct access_coordinate coord[ACCESS_COORDINATE_MAX];
 	struct notifier_block memory_notifier;
+	struct notifier_block adist_notifier;
 };
 
 struct cxl_nvdimm_bridge {