2 files changed, 5 insertions, 8 deletions

diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt
index e566affeed7f..72ab9b99b22c 100644
--- a/Documentation/x86_64/boot-options.txt
+++ b/Documentation/x86_64/boot-options.txt
@@ -125,7 +125,7 @@ SMP
   cpumask=MASK   only use cpus with bits set in mask
 
   additional_cpus=NUM Allow NUM more CPUs for hotplug
-                 (defaults are specified by the BIOS or half the available CPUs)
+                 (defaults are specified by the BIOS, see Documentation/x86_64/cpu-hotplug-spec)
 
 NUMA
 
diff --git a/arch/x86_64/kernel/smpboot.c b/arch/x86_64/kernel/smpboot.c
index ecbd7b83acc1..043b1d262a30 100644
--- a/arch/x86_64/kernel/smpboot.c
+++ b/arch/x86_64/kernel/smpboot.c
@@ -927,8 +927,8 @@ int additional_cpus __initdata = -1;
  *
  * Three ways to find out the number of additional hotplug CPUs:
  * - If the BIOS specified disabled CPUs in ACPI/mptables use that.
- * - otherwise use half of the available CPUs or 2, whatever is more.
  * - The user can overwrite it with additional_cpus=NUM
+ * - Otherwise don't reserve additional CPUs.
  * We do this because additional CPUs waste a lot of memory.
  * -AK
  */
@@ -938,13 +938,10 @@ __init void prefill_possible_map(void)
         int possible;
 
         if (additional_cpus == -1) {
-                if (disabled_cpus > 0) {
+                if (disabled_cpus > 0)
                         additional_cpus = disabled_cpus;
-                } else {
-                        additional_cpus = num_processors / 2;
-                        if (additional_cpus == 0)
-                                additional_cpus = 2;
-                }
+                else
+                        additional_cpus = 0;
         }
         possible = num_processors + additional_cpus;
         if (possible > NR_CPUS)