From e63190c9c02a5ce17f6ceb1131f1c6083ef182b0 Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Wed, 11 Jan 2006 22:42:39 +0100 Subject: [PATCH] --- yaml --- r: 17931 b: refs/heads/master c: 7eb903f4a5c35c8310f0aa7b0e94aae0b826d837 h: refs/heads/master i: 17929: 6d13cd51633cffcc1fb7cd46a2b0e22763e45399 17927: 4e53dec02392035ce701949d898ac5da48ce4cf3 v: v3 --- [refs] | 2 +- trunk/Documentation/x86_64/cpu-hotplug-spec | 21 +++++++++++++++++++++ 2 files changed, 22 insertions(+), 1 deletion(-) create mode 100644 trunk/Documentation/x86_64/cpu-hotplug-spec diff --git a/[refs] b/[refs] index 7851af4c152a..106cbfe79764 100644 --- a/[refs] +++ b/[refs] @@ -1,2 +1,2 @@ --- -refs/heads/master: f62a91f6911479642c0018290d4248ace4287648 +refs/heads/master: 7eb903f4a5c35c8310f0aa7b0e94aae0b826d837 diff --git a/trunk/Documentation/x86_64/cpu-hotplug-spec b/trunk/Documentation/x86_64/cpu-hotplug-spec new file mode 100644 index 000000000000..5c0fa345e556 --- /dev/null +++ b/trunk/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.