smp: Use nr_cpus= to set nr_cpu_ids early

On x86, before prefill_possible_map(), nr_cpu_ids will be NR_CPUS aka
CONFIG_NR_CPUS.

Add nr_cpus= to set nr_cpu_ids. so we can simulate cpus <=8 are installed on
normal config.

-v2: accordging to Christoph, acpi_numa_init should use nr_cpu_ids in stead of
     NR_CPUS.
-v3: add doc in kernel-parameters.txt according to Andrew.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <1265793639-15071-34-git-send-email-yinghai@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Tony Luck <tony.luck@intel.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 678d0b8c26f3..eff2fe175422 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1213,11 +1213,12 @@ __init void prefill_possible_map(void)
 
         total_cpus = max_t(int, possible, num_processors + disabled_cpus);
 
-        if (possible > CONFIG_NR_CPUS) {
+        /* nr_cpu_ids could be reduced via nr_cpus= */
+        if (possible > nr_cpu_ids) {
                 printk(KERN_WARNING
                         "%d Processors exceeds NR_CPUS limit of %d\n",
-                        possible, CONFIG_NR_CPUS);
-                possible = CONFIG_NR_CPUS;
+                        possible, nr_cpu_ids);
+                possible = nr_cpu_ids;
         }
 
         printk(KERN_INFO "SMP: Allowing %d CPUs, %d hotplug CPUs\n",