Hello, and welcome!
Can you control CPU speed with
apmd(8) and
apm(8), which are used to manage the
hw.setperf sysctl?
OpenBSD's _PPC listener is a component of the
acpicpu(4) driver. This driver has no flags that can be set with
config(8), but config(8) could be used to disable the driver ... which might cause operational malfunctions and risks damage to your hardware.
If you're interested in modifying the driver yourself, the driver can be found in src/sys/dev/acpi/acpicpu.c, while guidance for obtaining the source and for kernel building can be found in FAQ 5
.
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(You've posted in a FreeBSD subforum, but I'm sure one of the admins will move the thread for you.)