x86: convert cpu_to_apicid to be a per cpu variable

This patch converts the x86_cpu_to_apicid array to be a per cpu
variable. This saves sizeof(apicid) * NR unused cpus.  Access is mostly
from startup and CPU HOTPLUG functions.

MP_processor_info() is one of the functions that require access to the
x86_cpu_to_apicid array before the per_cpu data area is setup.  For this
case, a pointer to the __initdata array is initialized in setup_arch()
and removed in smp_prepare_cpus() after the per_cpu data area is
initialized.

A second change is included to change the initial array value of ARCH
i386 from 0xff to BAD_APICID to be consistent with ARCH x86_64.

Signed-off-by: Mike Travis <travis@sgi.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 15 insertions, 7 deletions

diff --git a/arch/x86/kernel/smpboot_32.c b/arch/x86/kernel/smpboot_32.c
index 65e5de7d64db..631be36ec2a9 100644
--- a/arch/x86/kernel/smpboot_32.c
+++ b/arch/x86/kernel/smpboot_32.c
@@ -92,9 +92,17 @@ static cpumask_t smp_commenced_mask;
 struct cpuinfo_x86 cpu_data[NR_CPUS] __cacheline_aligned;
 EXPORT_SYMBOL(cpu_data);
 
-u8 x86_cpu_to_apicid[NR_CPUS] __read_mostly =
-                        { [0 ... NR_CPUS-1] = 0xff };
-EXPORT_SYMBOL(x86_cpu_to_apicid);
+/*
+ * The following static array is used during kernel startup
+ * and the x86_cpu_to_apicid_ptr contains the address of the
+ * array during this time.  Is it zeroed when the per_cpu
+ * data area is removed.
+ */
+u8 x86_cpu_to_apicid_init[NR_CPUS] __initdata =
+                        { [0 ... NR_CPUS-1] = BAD_APICID };
+void *x86_cpu_to_apicid_ptr;
+DEFINE_PER_CPU(u8, x86_cpu_to_apicid) = BAD_APICID;
+EXPORT_PER_CPU_SYMBOL(x86_cpu_to_apicid);
 
 u8 apicid_2_node[MAX_APICID];
 
@@ -804,7 +812,7 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu)
 
         irq_ctx_init(cpu);
 
-        x86_cpu_to_apicid[cpu] = apicid;
+        per_cpu(x86_cpu_to_apicid, cpu) = apicid;
         /*
          * This grunge runs the startup process for
          * the targeted processor.
@@ -866,7 +874,7 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu)
                 cpu_clear(cpu, cpu_initialized); /* was set by cpu_init() */
                 cpucount--;
         } else {
-                x86_cpu_to_apicid[cpu] = apicid;
+                per_cpu(x86_cpu_to_apicid, cpu) = apicid;
                 cpu_set(cpu, cpu_present_map);
         }
 
@@ -915,7 +923,7 @@ static int __cpuinit __smp_prepare_cpu(int cpu)
         struct warm_boot_cpu_info info;
         int     apicid, ret;
 
-        apicid = x86_cpu_to_apicid[cpu];
+        apicid = per_cpu(x86_cpu_to_apicid, cpu);
         if (apicid == BAD_APICID) {
                 ret = -ENODEV;
                 goto exit;
@@ -965,7 +973,7 @@ static void __init smp_boot_cpus(unsigned int max_cpus)
 
         boot_cpu_physical_apicid = GET_APIC_ID(apic_read(APIC_ID));
         boot_cpu_logical_apicid = logical_smp_processor_id();
-        x86_cpu_to_apicid[0] = boot_cpu_physical_apicid;
+        per_cpu(x86_cpu_to_apicid, 0) = boot_cpu_physical_apicid;
 
         current_thread_info()->cpu = 0;