.\"	$OpenBSD: cpu.4,v 1.20 2024/09/10 17:01:09 tb Exp $
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.\" Copyright (c) 2004 Ted Unangst
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.Dd $Mdocdate: September 10 2024 $
.Dt CPU 4 i386
.Os
.Sh NAME
.Nm cpu
.Nd Central Processing Unit
.Sh SYNOPSIS
.Cd "cpu0 at mainbus?"
.Cd "cpu* at mainbus?"
.Sh DESCRIPTION
Several processor models have additional features that extend their base
functionality, such as power and frequency control or thermal monitoring.
.Pp
The
.Xr sysctl 2
.Va 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
.Va hw.setperf
from 0 to 100,
representing percentage of maximum speed.
.Pp
There are several possible implementations for speed adjustment,
all transparent to the user.
In systems with more than one control capability, they are preferred in the
order given:
.Bl -tag -width tenletters
.It LongRun
Found on Transmeta Crusoe processors, offering frequency scaling with numerous
positions.
The processor dynamically adjusts frequency in response to load; the setperf
value is interpreted as the maximum.
.It EST
Enhanced SpeedStep found on Intel Pentium M processors,
offering frequency scaling with numerous positions.
.It SpeedStep
Found on some Intel Pentium 3 and newer mobile chips,
it is capable of adjusting frequency between a low and high value.
It is only enabled on some chipsets.
.It TCC
Thermal Control Circuit found on Intel Pentium 4 and newer processors,
it can adjust processor duty cycle in 12.5 percent increments.
.It PowerNow
Found on various AMD processors.
It currently only supports a limited set of models
in the K6, K7, and K8 families.
.El
.Pp
The presence of extended instruction sets can be determined by the sysctl
.Va machdep :
.Bl -tag -width "tenletters"
.It osfxsr
Supports the fxsave instruction.
.It sse
Supports the SSE instruction set.
.It sse2
Supports the SSE2 instruction set.
.It xcrypt
Supports the VIA AES encryption instruction set.
.El
.Pp
The sysctl
.Va hw.sensors
returns the current temperature reported by the processor.
.Sh SEE ALSO
.Xr sysctl 8
.Sh BUGS
Due to the way in which thermal information is reported on Intel processors,
the temperature may be off by exactly +/-15 degrees C.
.Pp
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.