---
name: "acpicpu"
section: "4"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["openbsd"]
url: "https://new.carta.tech/acpicpu"
---

# acpicpu(4)

ACPI processor power and performance state

## NAME

**acpicpu** – ACPI processor power and performance state

## SYNOPSIS

**acpicpu\* at acpi?**

## DESCRIPTION

The **acpicpu** driver provides support for extracting processor power and performance levels from ACPI tables. This information is used to enter deeper CPU power states when idle, and can be used to throttle processor speed to reduce power usage and extend battery life through the *hw.setperf* [sysctl(2)](/sysctl/2.md) mechanism.

**acpicpu** reports the C-states offered by ACPI using the format

```
C%d(%d@%d %s.%x@%#x)
```

where the respective fields are the ACPI state, the reported power consumption, the reported latency, the method, the flags on the method, and the address for the method. Inapplicable or unspecified fields are elided. If the state won't be used for any reason then the entry will have a ‘!’ prefix. If the state is the fallback state used when no valid C-state entries were found then flags will be a ‘!’. For the *mwait* method the address is the hints value for the instruction.

## SEE ALSO

[sysctl(2)](/sysctl/2.md), [acpi(4)](/acpi/4.md), [cpu(4)](/cpu/4.md), [intro(4)](/intro/4.md), [apmd(8)](/apmd/8.md), [sysctl(8)](/sysctl/8.md)

## HISTORY

The **acpicpu** driver first appeared in OpenBSD 3.9.

## AUTHORS

The **acpicpu** driver was written by Marco Peereboom ⟨*marco@openbsd.org*⟩. CPU power state (C-state) support was added by Philip Guenther ⟨*guenther@openbsd.org*⟩.