It's not used to discover processors by OSes because typically that is done well before the AML interpreter is brought online. Instead it is used to describe how to control processor performance and thermal management (what ACPI calls C-states, P-states, and T-states on older systems, or CPPC on newer systems). How processors are discovered is platform dependent, but at least for x86/Arm/RISC-V you would parse the ACPI MADT to find these early at boot. Each processor has a unique ID in firmware that lets you associate an (optional) processor device node with the processor definition in the MADT.
The error message you are seeing comes from an (ill conceived IMHO) option ACPI_ACTIVATE_DEV which is not enabled by default in any kernels we ship. Each device node is going to have a _STA method that tells the OS whether that device is enabled. Because updating AML dynamically can be difficult, it's not uncommon for firmware to create templates for all possible processors and the _STA method will inspect some variable set early at boot to determine whether or not a given processor device is present.
So tl;dr: - Your firmware says "There is no processor device here" - Your kernel config says "Let me try anyway" and asks firmware to enable the device. - Firmware says no. - You get an error message logged. HTH, Jared On Sat, 5 Nov 2022, Robert Elz wrote:
This is just (well mostly) curiosity, it doesn't seem to affect anything that I know about, but during autoconfig, the kernel (any 9.99.x I have tried I think) prints acpi0: autoconfiguration error: failed to activate ACPI0007 64 times during the boot sequence (this one is from 9.99.105) I was just wondering what I apparently have so much of that this would appear so often (the other "failed to activate" messages I get seem to just occur once). The only thing that I'm aware of that I have 64 of is 64GB ram, but that's on just 2 DIMMs, and it is hard to believe that something is existing for each individual GB. Before I actually counted, when I just watched them scroll past (very quickly) during the boot, I guessed that it was perhaps once per CPU, but 64 CPUs, no matter how you count them, is way more than I have, so I doubt it is that. Anyone know ACPI well enough to know what that is? kre