diff options
| author | Ingo Molnar <mingo@elte.hu> | 2008-07-16 00:29:07 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2008-07-16 00:29:07 +0200 |
| commit | 82638844d9a8581bbf33201cc209a14876eca167 (patch) | |
| tree | 961d7f9360194421a71aa644a9d0c176a960ce49 /Documentation/x86/x86_64/cpu-hotplug-spec | |
| parent | Revert "cpumask: introduce new APIs" (diff) | |
| parent | generic ipi function calls: wait on alloc failure fallback (diff) | |
| download | linux-82638844d9a8581bbf33201cc209a14876eca167.tar.xz linux-82638844d9a8581bbf33201cc209a14876eca167.zip | |
Merge branch 'linus' into cpus4096
Conflicts:
arch/x86/xen/smp.c
kernel/sched_rt.c
net/iucv/iucv.c
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'Documentation/x86/x86_64/cpu-hotplug-spec')
| -rw-r--r-- | Documentation/x86/x86_64/cpu-hotplug-spec | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/Documentation/x86/x86_64/cpu-hotplug-spec b/Documentation/x86/x86_64/cpu-hotplug-spec new file mode 100644 index 000000000000..3c23e0587db3 --- /dev/null +++ b/Documentation/x86/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 of 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. |