[PATCH v2] x86/apic: Use smaller array for __apicid_to_node[] mapping

[Daniel J Blueman <daniel@numascale.com>]

The Intel x2APIC spec states the upper 16-bits of APIC ID is the
cluster ID [1, p2-12], intended for future distributed systems. Beyond
the legacy 8-bit APIC ID, Numascale NumaConnect uses 4-bits for the
position of a server on each axis of a multi-dimension torus; SGI
NUMAlink also structures the APIC ID space.

Instead, define an array based on NR_CPUs to achieve a 1:1 mapping and
perform linear search; we see "ACPI: NR_CPUS/possible_cpus limit of X
reached.  Processor 8/0x16 ignored." when config-limited. This addresses
the binary bloat and the present artificial APIC ID limits. With
CONFIG_NR_CPUS=256, we save ~64KB of vmlinux data:

$ size vmlinux vmlinux-patched
  text      data     bss      dec     hex filename
18232877 1849656 2281472 22364005 1553f65 vmlinux
18233034 1786168 2281472 22300674 1544802 vmlinux-patched

Tested on a 256-core system with a 20-bit APIC ID space, and on a
48-core legacy 8-bit APIC ID system with and without CONFIG_NUMA,
CONFIG_NUMA_EMU and CONFIG_AMD_NUMA.

v2: Improved readability by moving static variable out; integrated Denys's
numa emulation fix

Signed-off-by: Daniel J Blueman <daniel@numascale.com>
CC: Denys Vlasenko <dvlasenk@redhat.com>
CC: Ingo Molnar <mingo@kernel.org>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Jiang Liu <jiang.liu@linux.intel.com>
CC: Len Brown <len.brown@intel.com>
CC: Steffen Persvold <sp@numascale.com>
CC: linux-kernel@vger.kernel.org
CC: x86@kernel.org

[1] http://www.intel.com/content/dam/doc/specification-update/64-architecture-x2apic-specification.pdf
---
 arch/x86/include/asm/numa.h  | 13 +++++++------
 arch/x86/kernel/cpu/amd.c    | 11 ++++++-----
 arch/x86/mm/numa.c           | 29 +++++++++++++++++++++--------
 arch/x86/mm/numa_emulation.c |  6 +++---
 4 files changed, 37 insertions(+), 22 deletions(-)

diff --git a/arch/x86/include/asm/numa.h b/arch/x86/include/asm/numa.h
index 01b493e..33becb8 100644
--- a/arch/x86/include/asm/numa.h
+++ b/arch/x86/include/asm/numa.h
@@ -17,6 +17,11 @@
  */
 #define NODE_MIN_SIZE (4*1024*1024)
 
+struct apicid_to_node {
+	int apicid;
+	s16 node;
+};
+
 extern int numa_off;
 
 /*
@@ -27,17 +32,13 @@ extern int numa_off;
  * should be accessed by the accessors - set_apicid_to_node() and
  * numa_cpu_node().
  */
-extern s16 __apicid_to_node[MAX_LOCAL_APIC];
+extern struct apicid_to_node __apicid_to_node[NR_CPUS];
 extern nodemask_t numa_nodes_parsed __initdata;
 
 extern int __init numa_add_memblk(int nodeid, u64 start, u64 end);
 extern void __init numa_set_distance(int from, int to, int distance);
 
-static inline void set_apicid_to_node(int apicid, s16 node)
-{
-	__apicid_to_node[apicid] = node;
-}
-
+extern void set_apicid_to_node(int apicid, s16 node);
 extern int numa_cpu_node(int cpu);
 
 #else	/* CONFIG_NUMA */
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 4a70fc6..9494f0e 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -277,12 +277,13 @@ static int nearby_node(int apicid)
 	int i, node;
 
 	for (i = apicid - 1; i >= 0; i--) {
-		node = __apicid_to_node[i];
+		node = __apicid_to_node[i].node;
 		if (node != NUMA_NO_NODE && node_online(node))
 			return node;
 	}
-	for (i = apicid + 1; i < MAX_LOCAL_APIC; i++) {
-		node = __apicid_to_node[i];
+	for (i = apicid + 1; i < NR_CPUS; i++) {
+		node = __apicid_to_node[i].node;
+
 		if (node != NUMA_NO_NODE && node_online(node))
 			return node;
 	}
@@ -422,8 +423,8 @@ static void srat_detect_node(struct cpuinfo_x86 *c)
 		int ht_nodeid = c->initial_apicid;
 
 		if (ht_nodeid >= 0 &&
-		    __apicid_to_node[ht_nodeid] != NUMA_NO_NODE)
-			node = __apicid_to_node[ht_nodeid];
+		    __apicid_to_node[ht_nodeid].node != NUMA_NO_NODE)
+			node = __apicid_to_node[ht_nodeid].node;
 		/* Pick a nearby node */
 		if (!node_online(node))
 			node = nearby_node(apicid);
diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
index c3b3f65..849a113 100644
--- a/arch/x86/mm/numa.c
+++ b/arch/x86/mm/numa.c
@@ -26,6 +26,7 @@ nodemask_t numa_nodes_parsed __initdata;
 struct pglist_data *node_data[MAX_NUMNODES] __read_mostly;
 EXPORT_SYMBOL(node_data);
 
+static unsigned apicids;
 static struct numa_meminfo numa_meminfo
 #ifndef CONFIG_MEMORY_HOTPLUG
 __initdata
@@ -56,16 +57,31 @@ early_param("numa", numa_setup);
 /*
  * apicid, cpu, node mappings
  */
-s16 __apicid_to_node[MAX_LOCAL_APIC] = {
-	[0 ... MAX_LOCAL_APIC-1] = NUMA_NO_NODE
+struct apicid_to_node __apicid_to_node[NR_CPUS] = {
+	[0 ... NR_CPUS-1] = {-1, NUMA_NO_NODE}
 };
 
+void set_apicid_to_node(int apicid, s16 node)
+{
+	/* Protect against small kernel on large system */
+	if (apicids >= NR_CPUS)
+		return;
+
+	__apicid_to_node[apicids].apicid = apicid;
+	__apicid_to_node[apicids].node = node;
+	apicids++;
+}
+
 int numa_cpu_node(int cpu)
 {
-	int apicid = early_per_cpu(x86_cpu_to_apicid, cpu);
+	int ent, apicid = early_per_cpu(x86_cpu_to_apicid, cpu);
+	if (apicid == BAD_APICID)
+		return NUMA_NO_NODE;
+
+	for (ent = 0; ent < NR_CPUS; ent++)
+		if (__apicid_to_node[ent].apicid == apicid)
+			return __apicid_to_node[ent].node;
 
-	if (apicid != BAD_APICID)
-		return __apicid_to_node[apicid];
 	return NUMA_NO_NODE;
 }
 
@@ -607,9 +623,6 @@ static int __init numa_init(int (*init_func)(void))
 	int i;
 	int ret;
 
-	for (i = 0; i < MAX_LOCAL_APIC; i++)
-		set_apicid_to_node(i, NUMA_NO_NODE);
-
 	nodes_clear(numa_nodes_parsed);
 	nodes_clear(node_possible_map);
 	nodes_clear(node_online_map);
diff --git a/arch/x86/mm/numa_emulation.c b/arch/x86/mm/numa_emulation.c
index a8f90ce..1a0e112 100644
--- a/arch/x86/mm/numa_emulation.c
+++ b/arch/x86/mm/numa_emulation.c
@@ -399,12 +399,12 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
 	 * back to zero just in case.
 	 */
 	for (i = 0; i < ARRAY_SIZE(__apicid_to_node); i++) {
-		if (__apicid_to_node[i] == NUMA_NO_NODE)
+		if (__apicid_to_node[i].node == NUMA_NO_NODE)
 			continue;
 		for (j = 0; j < ARRAY_SIZE(emu_nid_to_phys); j++)
-			if (__apicid_to_node[i] == emu_nid_to_phys[j])
+			if (__apicid_to_node[i].node == emu_nid_to_phys[j])
 				break;
-		__apicid_to_node[i] = j < ARRAY_SIZE(emu_nid_to_phys) ? j : 0;
+		__apicid_to_node[i].node = j < ARRAY_SIZE(emu_nid_to_phys) ? j : 0;
 	}
 
 	/* make sure all emulated nodes are mapped to a physical node */
-- 
2.5.0