[PATCH] x86_64: Don't reserve hotplug CPUs by default
Most users don't need it so no need to waste memory.
This means an user has to specify the appropiate number of
hotplug CPUs on the command line with additional_cpus=...
or fix their BIOS to follow the convention in
Documentation/x86-64/cpu-hotplug-spec
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt
index e566aff..72ab9b9 100644
--- a/Documentation/x86_64/boot-options.txt
+++ b/Documentation/x86_64/boot-options.txt
@@ -125,7 +125,7 @@
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 ecbd7b8..043b1d2 100644
--- a/arch/x86_64/kernel/smpboot.c
+++ b/arch/x86_64/kernel/smpboot.c
@@ -927,8 +927,8 @@
*
* 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 @@
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)