Comment 53 for bug 1973434

I found a solution for this, at least for my case! I traced the CPU pinning to ACPI GPE11 (corresponding to IRQ9 in my Mac Pro 1,1) being hit constantly.

This can be killed permanently by passing "acpi_mask_gpe=0x11" to the kernel at boot.

I still believe this was first triggered for 20.04 first during the generic 5.11-5.13 transition and then later during the low-latency 5.13-5.15 transition using the official Ubuntu kernels. I still haven't been able to pinpoint if this was a config change's fault, or perhaps whether a microcode error crept in.

Suggest people give this a go. It clearly works for some others. For more background see here:
https://unix.stackexchange.com/questions/588018/kworker-thread-kacpid-notify-kacpid-hogging-60-70-of-cpu

Also a couple of posts here:
https://mattgadient.com/linux-dvd-images-and-how-to-for-32-bit-efi-macs-late-2006-models/