x86, apic: Use logical flat on intel with <= 8 logical cpus

On Intel platforms, we can use logical flat mode if there are <= 8
logical cpu's (irrespective of physical apic id values). This will
enable simplified and efficient IPI and device interrupt routing on
such platforms.

Fix the relevant comments while we are at it.

We can clean up default_setup_apic_routing() by using apic->probe()
but that is a different item.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: "yinghai@kernel.org" <yinghai@kernel.org>
LKML-Reference: <1253327399.3948.747.camel@sbs-t61.sc.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 11 insertions, 4 deletions

diff --git a/arch/x86/kernel/apic/probe_64.c b/arch/x86/kernel/apic/probe_64.c
index 65edc180fc82..c4cbd3080c1c 100644
--- a/arch/x86/kernel/apic/probe_64.c
+++ b/arch/x86/kernel/apic/probe_64.c
@@ -64,16 +64,23 @@ void __init default_setup_apic_routing(void)
                         apic = &apic_x2apic_phys;
                 else
                         apic = &apic_x2apic_cluster;
-                printk(KERN_INFO "Setting APIC routing to %s\n", apic->name);
         }
 #endif
 
         if (apic == &apic_flat) {
-                if (max_physical_apicid >= 8)
-                        apic = &apic_physflat;
-                printk(KERN_INFO "Setting APIC routing to %s\n", apic->name);
+                switch (boot_cpu_data.x86_vendor) {
+                case X86_VENDOR_INTEL:
+                        if (num_processors > 8)
+                                apic = &apic_physflat;
+                        break;
+                case X86_VENDOR_AMD:
+                        if (max_physical_apicid >= 8)
+                                apic = &apic_physflat;
+                }
         }
 
+        printk(KERN_INFO "Setting APIC routing to %s\n", apic->name);
+
         if (is_vsmp_box()) {
                 /* need to update phys_pkg_id */
                 apic->phys_pkg_id = apicid_phys_pkg_id;