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.\" $OpenBSD: acpicpu.4,v 1.10 2022/10/21 04:02:16 guenther Exp $
.\"
.\" Copyright (c) 2006 Michael Knudsen <mk@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: October 21 2022 $
.Dt ACPICPU 4
.Os
.Sh NAME
.Nm acpicpu
.Nd ACPI processor power and performance state
.Sh SYNOPSIS
.Cd "acpicpu* at acpi?"
.Sh DESCRIPTION
The
.Nm
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
.Va hw.setperf
.Xr sysctl 2
mechanism.
.Pp
.Nm
reports the C-states offered by ACPI using the format
.Dl 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
.Sq !\&
prefix.
If the state is the fallback state used when no valid C-state entries were
found then flags will be a
.Sq !\& .
For the
.Va mwait
method the address is the hints value for the instruction.
.Sh SEE ALSO
.Xr sysctl 2 ,
.Xr acpi 4 ,
.Xr cpu 4 ,
.Xr intro 4 ,
.Xr apmd 8 ,
.Xr sysctl 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Ox 3.9 .
.Sh AUTHORS
.An -nosplit
The
.Nm
driver was written by
.An Marco Peereboom Aq Mt marco@openbsd.org .
CPU power state (C-state) support was added by
.An Philip Guenther Aq Mt guenther@openbsd.org .
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