[PATCH] x86_64: Early initialization of cpu_to_node

Patch enables early intialization of cpu_to_node.
apicid_to_node is built by reading the SRAT table, from acpi_numa_init with
ACPI_NUMA and k8_scan_nodes with K8_NUMA.
x86_cpu_to_apicid is built by parsing the ACPI MADT table, from acpi_boot_init.
We combine these two tables and setup cpu_to_node.

Early intialization helps the static per_cpu_areas in getting pages from
correct node.

Change since last release:
Do not initialize early init_cpu_to_node for faking node cases.

Patch tested on TYAN dual core 4P board with K8 only, ACPI_NUMA.
Tested on EM64T NUMA. Also tested with numa=off, numa=fake, and running
a kernel compiled with NUMA on a regular EM64 2 way SMP.

Signed-off-by: Alok N Kataria <[e-mail]>
Signed-off-by: Ravikiran Thirumalai <[e-mail]>
Signed-off-by: Shai Fultheim <[e-mail]>
Signed-off-by: Andi Kleen <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/x86_64/kernel/setup.c

···
 	acpi_boot_init();
 #endif
 
+	init_cpu_to_node();
+
 #ifdef CONFIG_X86_LOCAL_APIC
 	/*
 	 * get boot-time SMP configuration:

arch/x86_64/mm/numa.c

···
 	return 1;
 } 
 
+/*
+ * Setup early cpu_to_node.
+ *
+ * Populate cpu_to_node[] only if x86_cpu_to_apicid[],
+ * and apicid_to_node[] tables have valid entries for a CPU.
+ * This means we skip cpu_to_node[] initialisation for NUMA
+ * emulation and faking node case (when running a kernel compiled
+ * for NUMA on a non NUMA box), which is OK as cpu_to_node[]
+ * is already initialized in a round robin manner at numa_init_array,
+ * prior to this call, and this initialization is good enough
+ * for the fake NUMA cases.
+ */
+void __init init_cpu_to_node(void)
+{
+	int i;
+ 	for (i = 0; i < NR_CPUS; i++) {
+		u8 apicid = x86_cpu_to_apicid[i];
+		if (apicid == BAD_APICID)
+			continue;
+		if (apicid_to_node[apicid] == NUMA_NO_NODE)
+			continue;
+ 		cpu_to_node[i] = apicid_to_node[apicid];
+	}
+}
+
 EXPORT_SYMBOL(cpu_to_node);
 EXPORT_SYMBOL(node_to_cpumask);
 EXPORT_SYMBOL(memnode_shift);

include/asm-x86_64/numa.h

···
 extern void numa_set_node(int cpu, int node);
 
 extern unsigned char apicid_to_node[256];
+#ifdef CONFIG_NUMA
+extern void __init init_cpu_to_node(void);
+#else
+#define init_cpu_to_node() do {} while (0)
+#endif
 
 #define NUMA_NO_NODE 0xff