CPU(4) | Device Drivers Manual (amd64) | CPU(4)

# NAME

`cpu` — Central Processing Unit

# SYNOPSIS

`cpu0 at mainbus?`
`cpu* at mainbus?`

# DESCRIPTION

Several processor models have additional features that extend their base functionality, such as power and frequency control or thermal monitoring.

The sysctl(2) hw.cpuspeed returns the current operating frequency of the processor, though on some processors this value may be only an approximation. If possible, speed may be adjusted by altering hw.setperf from 0 to 100, representing percentage of maximum speed.

There are several possible implementations for speed adjustment, all transparent to the user:

EST
  Enhanced SpeedStep found on Intel and VIA processors, offering frequency scaling with numerous positions.
PowerNow
  Found on various AMD processors. It currently only supports a limited set of models in the K8 families.

The presence of extended instruction sets can be determined by the sysctl machdep:

xcrypt
  Supports the VIA AES encryption instruction set.

The sysctl hw.sensors returns the current temperature reported by the processor.

# SEE ALSO

sysctl(8)

# BUGS

Due to the way in which thermal information is reported on Intel processors, the temperature may be off by exactly +/-15 degrees C.

For multiprocessor kernels with more than one CPU sensor, processors report identical temperatures since the temperature is taken from the processor running the sensors update.

September 10, 2024 | Debian