Documentation/arch/x86/x86_64/cpu-hotplug-spec.rst
Source file repositories/reference/linux-study-clean/Documentation/arch/x86/x86_64/cpu-hotplug-spec.rst
File Facts
- System
- Linux kernel
- Corpus path
Documentation/arch/x86/x86_64/cpu-hotplug-spec.rst- Extension
.rst- Size
- 1244 bytes
- Lines
- 25
- Domain
- Support Tooling And Documentation
- Bucket
- Documentation
- Inferred role
- Support Tooling And Documentation: documentation
- Status
- atlas-only
Why This File Exists
Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.
- Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.
Dependency Surface
- No C-style include directives detected by the generator.
Detected Declarations
- No top-level syscall, struct, function, initcall, or export declaration detected by the generator.
Annotated Snippet
.. SPDX-License-Identifier: GPL-2.0
===================================================
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.Annotation
- Atlas domain: Support Tooling And Documentation / Documentation.
- Implementation status: atlas-only.
Implementation Notes
- This generated page is the file-by-file coverage layer; curated subsystem chapters should link here when they synthesize a multi-file control flow.
- Core OS pages should be promoted from atlas-only to deep-reviewed when they explain data structures, invariants, locking, lifecycle, and C implementation snippets.
- Driver-family pages are intentionally pattern-oriented unless they are part of the selected PCIe/NVMe representative device path.