diff options
Diffstat (limited to 'Documentation/x86_64')
| -rw-r--r-- | Documentation/x86_64/boot-options.txt | 4 | ||||
| -rw-r--r-- | Documentation/x86_64/cpu-hotplug-spec | 21 |
2 files changed, 23 insertions, 2 deletions
diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt index e566affeed7..9c5fc15d03d 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 @@ -198,6 +198,6 @@ Debugging Misc - noreplacement Don't replace instructions with more appropiate ones + noreplacement Don't replace instructions with more appropriate ones for the CPU. This may be useful on asymmetric MP systems where some CPU have less capabilities than the others. diff --git a/Documentation/x86_64/cpu-hotplug-spec b/Documentation/x86_64/cpu-hotplug-spec new file mode 100644 index 00000000000..5c0fa345e55 --- /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. |