[PATCH] x86_64: Support more than 8 cores on AMD systems

Use physical mode instead of logical mode to address more CPUs.  This is also
used in the CPU hotplug case to avoid a race.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 24 insertions, 9 deletions

diff --git a/arch/x86_64/kernel/genapic.c b/arch/x86_64/kernel/genapic.c
index 69b9c25a8fc..30c843a5efd 100644
--- a/arch/x86_64/kernel/genapic.c
+++ b/arch/x86_64/kernel/genapic.c
@@ -31,6 +31,7 @@ u8 x86_cpu_to_log_apicid[NR_CPUS] = { [0 ... NR_CPUS-1] = BAD_APICID };
 
 extern struct genapic apic_cluster;
 extern struct genapic apic_flat;
+extern struct genapic apic_physflat;
 
 struct genapic *genapic = &apic_flat;
 
@@ -44,12 +45,7 @@ void __init clustered_apic_check(void)
 	u8 clusters, max_cluster;
 	u8 id;
 	u8 cluster_cnt[NUM_APIC_CLUSTERS];
-
-	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) {
-		/* AMD always uses flat mode right now */
-		genapic = &apic_flat;
-		goto print;
-	}
+	int num_cpus = 0;
 
 #if defined(CONFIG_ACPI_BUS)
 	/*
@@ -64,15 +60,34 @@ void __init clustered_apic_check(void)
 #endif
 
 	memset(cluster_cnt, 0, sizeof(cluster_cnt));
-
 	for (i = 0; i < NR_CPUS; i++) {
 		id = bios_cpu_apicid[i];
-		if (id != BAD_APICID)
-			cluster_cnt[APIC_CLUSTERID(id)]++;
+		if (id == BAD_APICID)
+			continue;
+		num_cpus++;
+		cluster_cnt[APIC_CLUSTERID(id)]++;
 	}
 
+	/* Don't use clustered mode on AMD platforms. */
+ 	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) {
+		genapic = &apic_physflat;
+#ifndef CONFIG_CPU_HOTPLUG
+		/* In the CPU hotplug case we cannot use broadcast mode
+		   because that opens a race when a CPU is removed.
+		   Stay at physflat mode in this case.
+		   It is bad to do this unconditionally though. Once
+		   we have ACPI platform support for CPU hotplug
+		   we should detect hotplug capablity from ACPI tables and
+		   only do this when really needed. -AK */
+		if (num_cpus <= 8)
+			genapic = &apic_flat;
+#endif
+ 		goto print;
+ 	}
+
 	clusters = 0;
 	max_cluster = 0;
+
 	for (i = 0; i < NUM_APIC_CLUSTERS; i++) {
 		if (cluster_cnt[i] > 0) {
 			++clusters;