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, 6 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 736d45602886..51bceb0fb277 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1772,6 +1772,12 @@ and is between 256 and 4096 characters. It is defined in the file
                         purges which is reported from either PAL_VM_SUMMARY or
                         SAL PALO.
 
+        nr_cpus=        [SMP] Maximum number of processors that an SMP kernel
+                        could support.  nr_cpus=n : n >= 1 limits the kernel to
+                        supporting 'n' processors. Later in runtime you can not
+                        use hotplug cpu feature to put more cpu back to online.
+                        just like you compile the kernel NR_CPUS=n
+
         nr_uarts=       [SERIAL] maximum number of UARTs to be registered.
 
         numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.