[PATCH v2 1/3] acpi: Add acpi_map_pxm_to_online_node()

[Toshi Kani <toshi.kani@hp.com>]

The kernel initializes CPU & memory's NUMA topology from ACPI
SRAT table.  Some other ACPI tables, such as NFIT and DMAR,
also contain proximity IDs for their device's NUMA topology.
This information can be used to improve performance of these
devices.

This patch introduces acpi_map_pxm_to_online_node(), which maps
a given pxm to an online node.  This allows ACPI device driver
modules to obtain a node from a device proximity ID.  Unlike
acpi_map_pxm_to_node(), this interface is guaranteed to return
an online node so that the caller module can use the node without
dealing with the node status.  A node may be offline when a device
proximity ID is unique, SRAT memory entry does not exist, or
NUMA is disabled (ex. numa_off on x86).

This patch also moves the pxm range check from acpi_get_node()
to acpi_map_pxm_to_node().

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
---
 drivers/acpi/numa.c  |   40 +++++++++++++++++++++++++++++++++++++---
 include/linux/acpi.h |    5 +++++
 2 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/numa.c b/drivers/acpi/numa.c
index 1333cbdc..a64947e 100644
--- a/drivers/acpi/numa.c
+++ b/drivers/acpi/numa.c
@@ -29,6 +29,8 @@
 #include <linux/errno.h>
 #include <linux/acpi.h>
 #include <linux/numa.h>
+#include <linux/nodemask.h>
+#include <linux/topology.h>
 
 #define PREFIX "ACPI: "
 
@@ -70,7 +72,12 @@ static void __acpi_map_pxm_to_node(int pxm, int node)
 
 int acpi_map_pxm_to_node(int pxm)
 {
-	int node = pxm_to_node_map[pxm];
+	int node;
+
+	if (pxm < 0 || pxm >= MAX_PXM_DOMAINS)
+		return NUMA_NO_NODE;
+
+	node = pxm_to_node_map[pxm];
 
 	if (node == NUMA_NO_NODE) {
 		if (nodes_weight(nodes_found_map) >= MAX_NUMNODES)
@@ -83,6 +90,35 @@ int acpi_map_pxm_to_node(int pxm)
 	return node;
 }
 
+/*
+ * Return an online node from a pxm.  This interface is intended for ACPI
+ * device drivers that obtain device NUMA topology from ACPI table, but
+ * do not initialize the node status.
+ */
+int acpi_map_pxm_to_online_node(int pxm)
+{
+	int node, n, dist, min_dist;
+
+	node = acpi_map_pxm_to_node(pxm);
+
+	if (node == NUMA_NO_NODE)
+		node = 0;
+
+	if (!node_online(node)) {
+		min_dist = INT_MAX;
+		for_each_online_node(n) {
+			dist = node_distance(node, n);
+			if (dist < min_dist) {
+				min_dist = dist;
+				node = n;
+			}
+		}
+	}
+
+	return node;
+}
+EXPORT_SYMBOL(acpi_map_pxm_to_online_node);
+
 static void __init
 acpi_table_print_srat_entry(struct acpi_subtable_header *header)
 {
@@ -328,8 +364,6 @@ int acpi_get_node(acpi_handle handle)
 	int pxm;
 
 	pxm = acpi_get_pxm(handle);
-	if (pxm < 0 || pxm >= MAX_PXM_DOMAINS)
-		return NUMA_NO_NODE;
 
 	return acpi_map_pxm_to_node(pxm);
 }
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index e4da5e3..1b3bbb1 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -289,8 +289,13 @@ extern void acpi_dmi_osi_linux(int enable, const struct dmi_system_id *d);
 extern void acpi_osi_setup(char *str);
 
 #ifdef CONFIG_ACPI_NUMA
+int acpi_map_pxm_to_online_node(int pxm);
 int acpi_get_node(acpi_handle handle);
 #else
+static inline int acpi_map_pxm_to_online_node(int pxm)
+{
+	return 0;
+}
 static inline int acpi_get_node(acpi_handle handle)
 {
 	return 0;