diff --git a/share/man/man4/acpicpu.4 b/share/man/man4/acpicpu.4
index 2f8e793cb99b..e2cbc092564b 100644
--- a/share/man/man4/acpicpu.4
+++ b/share/man/man4/acpicpu.4
@@ -1,4 +1,4 @@
-.\" $NetBSD: acpicpu.4,v 1.7 2010/08/10 06:10:16 wiz Exp $
+.\" $NetBSD: acpicpu.4,v 1.8 2010/08/11 17:28:59 jruoho Exp $
 .\"
 .\" Coyright (c) 2010 Jukka Ruohonen <jruohonen@iki.fi>
 .\" All rights reserved.
@@ -24,7 +24,7 @@
 .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 .\" POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd August 10, 2010
+.Dd August 11, 2010
 .Dt ACPICPU 4
 .Os
 .Sh NAME
@@ -197,6 +197,23 @@ It is possible to view the statistics by using
 .Fl e
 flag).
 Note that valid per-CPU data is available only for C-states.
+.Ss System information variables
+The
+.Nm
+driver uses the same
+.Xr sysctl 8
+controls for P-states as the ones provided by the kernel configuration
+.Xr options 4
+.Dv ENHANCED_SPEEDSTEP
+and
+.Dv POWERNOW_K8 .
+Depending on the processor vendor, the second-level node is either
+.Ic machdep.est
+or
+.Ic machdep.powernow .
+Please note that future versions of
+.Nm
+may however remove the system control variables without further notice.
 .Sh SEE ALSO
 .Xr acpi 4 ,
 .Xr cpu_idle 9