diff options
| author | Andi Kleen | 2006-01-11 22:42:39 +0100 |
|---|---|---|
| committer | Linus Torvalds | 2006-01-12 04:01:11 +0100 |
| commit | 7eb903f4a5c35c8310f0aa7b0e94aae0b826d837 (patch) | |
| tree | 39489c4edd583ae398d7987019a4ba7315bdfcee /Documentation | |
| parent | [PATCH] x86_64: Don't reserve hotplug CPUs by default (diff) | |
| download | kernel-qcow2-linux-7eb903f4a5c35c8310f0aa7b0e94aae0b826d837.tar.gz kernel-qcow2-linux-7eb903f4a5c35c8310f0aa7b0e94aae0b826d837.tar.xz kernel-qcow2-linux-7eb903f4a5c35c8310f0aa7b0e94aae0b826d837.zip | |
[PATCH] x86_64: Add documentation for CPU hotplug ACPI extension
Cc: len.brown@intel.com, ashok.ray@intel.com
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/x86_64/cpu-hotplug-spec | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/Documentation/x86_64/cpu-hotplug-spec b/Documentation/x86_64/cpu-hotplug-spec new file mode 100644 index 000000000000..5c0fa345e556 --- /dev/null +++ b/Documentation/x86_64/cpu-hotplug-spec @@ -0,0 +1,21 @@ +Firmware support for CPU hotplug under Linux/x86-64 +--------------------------------------------------- + +Linux/x86-64 supports CPU hotplug now. For various reasons Linux wants to +know in advance boot time the maximum number of CPUs that could be plugged +into the system. ACPI 3.0 currently has no official way to supply +this information from the firmware to the operating system. + +In ACPI each CPU needs an LAPIC object in the MADT table (5.2.11.5 in the +ACPI 3.0 specification). ACPI already has the concept of disabled LAPIC +objects by setting the Enabled bit in the LAPIC object to zero. + +For CPU hotplug Linux/x86-64 expects now that any possible future hotpluggable +CPU is already available in the MADT. If the CPU is not available yet +it should have its LAPIC Enabled bit set to 0. Linux will use the number +of disabled LAPICs to compute the maximum number of future CPUs. + +In the worst case the user can overwrite this choice using a command line +option (additional_cpus=...), but it is recommended to supply the correct +number (or a reasonable approximation of it, with erring towards more not less) +in the MADT to avoid manual configuration. |