x86, apic: use logical flat for systems with <= 8 logical cpus

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.

This has been tested to work on both Intel and AMD platforms.
Exceptions like IBM summit platform which can't use logical flat mode
are addressed by using OEM platform checks.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Chris McDermott <lcm@linux.vnet.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index e80f291472a4158535e44ed9afac24f8400453b8..3987e4408f75fc02266eb8ae805aef9831155f59 100644 (file)
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -61,12 +61,6 @@ unsigned int boot_cpu_physical_apicid = -1U;
 
 /*
  * The highest APIC ID seen during enumeration.
- *
- * This determines the messaging protocol we can use: if all APIC IDs
- * are in the 0 ... 7 range, then we can use logical addressing which
- * has some performance advantages (better broadcasting).
- *
- * If there's an APIC ID above 8, we use physical addressing.
  */
 unsigned int max_physical_apicid;
 
@@ -1898,14 +1892,7 @@ void __cpuinit generic_processor_info(int apicid, int version)
                max_physical_apicid = apicid;
 
 #ifdef CONFIG_X86_32
-       /*
-        * Would be preferable to switch to bigsmp when CONFIG_HOTPLUG_CPU=y
-        * but we need to work other dependencies like SMP_SUSPEND etc
-        * before this can be done without some confusion.
-        * if (CPU_HOTPLUG_ENABLED || num_processors > 8)
-        *       - Ashok Raj <ashok.raj@intel.com>
-        */
-       if (max_physical_apicid >= 8) {
+       if (num_processors > 8) {
                switch (boot_cpu_data.x86_vendor) {
                case X86_VENDOR_INTEL:
                        if (!APIC_XAPIC(version)) {

diff --git a/arch/x86/kernel/apic/probe_64.c b/arch/x86/kernel/apic/probe_64.c
index 65edc180fc8297be82347bec05e3cd62d155a86d..450fe2064a1411909b53e2e6ca818d446c4bca78 100644 (file)
--- a/arch/x86/kernel/apic/probe_64.c
+++ b/arch/x86/kernel/apic/probe_64.c
@@ -64,15 +64,13 @@ 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)
+       if (apic == &apic_flat && num_processors > 8)
                        apic = &apic_physflat;
-               printk(KERN_INFO "Setting APIC routing to %s\n", apic->name);
-       }
+
+       printk(KERN_INFO "Setting APIC routing to %s\n", apic->name);
 
        if (is_vsmp_box()) {
                /* need to update phys_pkg_id */