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| author |   Jonathan Corbet <corbet@lwn.net> | 2023-03-14 17:06:44 -0600 |
|---|---|---|
| committer | Jonathan Corbet <corbet@lwn.net> | 2023-03-30 12:58:51 -0600 |
| commit | ff61f0791ce969d2db6c9f3b71d74ceec0a2e958 (patch) | |
| tree | fe32be44aaf65f9c436a8f37cd4a18f6ec47c3cb /Documentation/arch/x86/x86_64/cpu-hotplug-spec.rst | |
| parent | Documentation: kernel-parameters: Remove meye entry (diff) | |
| download | wireguard-linux-ff61f0791ce969d2db6c9f3b71d74ceec0a2e958.tar.xz wireguard-linux-ff61f0791ce969d2db6c9f3b71d74ceec0a2e958.zip | |
docs: move x86 documentation into Documentation/arch/
Move the x86 documentation under Documentation/arch/ as a way of cleaning
up the top-level directory and making the structure of our docs more
closely match the structure of the source directories it describes.
All in-kernel references to the old paths have been updated.
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: linux-arch@vger.kernel.org
Cc: x86@kernel.org
Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/lkml/20230315211523.108836-1-corbet@lwn.net/
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/arch/x86/x86_64/cpu-hotplug-spec.rst')
| -rw-r--r-- | Documentation/arch/x86/x86_64/cpu-hotplug-spec.rst | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/Documentation/arch/x86/x86_64/cpu-hotplug-spec.rst b/Documentation/arch/x86/x86_64/cpu-hotplug-spec.rst new file mode 100644 index 000000000000..8d1c91f0c880 --- /dev/null +++ b/Documentation/arch/x86/x86_64/cpu-hotplug-spec.rst @@ -0,0 +1,24 @@ +.. 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. |