22 lines
1.1 KiB
Text
22 lines
1.1 KiB
Text
|
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.
|