add note about CPU P states

diff --git a/docs/user/Powersave.mdwn b/docs/user/Powersave.mdwn
index 32e7ccc..4a7ab55 100644 (file)
--- a/docs/user/Powersave.mdwn
+++ b/docs/user/Powersave.mdwn
@@ -47,6 +47,33 @@ In my Lenovo Thinkpad X61s relevant sysctl's look like this:
 
 Switching to minimums (frequency really doesn't matter in idle machine though) makes ~1.7W difference in power consumption in my idle laptop.
 
+## CPU P states 
+
+Alternatively to EST one can use CPU P states which make the frequency scaling features of the CPU accessible
+through a standardized interface.
+CPU P states work on multicore CPUs and the frequencies can be scaled individually depending on the hardware
+capabilities.
+
+The relevant sysctl's look like this on leaf.dragonflybsd.org:
+
+     $ sysctl hw.acpi.cpu | grep px
+     hw.acpi.cpu.px_dom3.available: 2600 1300
+     hw.acpi.cpu.px_dom3.members: cpu3(2600)
+     hw.acpi.cpu.px_dom3.select: 2600
+     hw.acpi.cpu.px_dom2.available: 2600 1300
+     hw.acpi.cpu.px_dom2.members: cpu2(2600)
+     hw.acpi.cpu.px_dom2.select: 2600
+     hw.acpi.cpu.px_dom1.available: 2600 1300
+     hw.acpi.cpu.px_dom1.members: cpu1(2600)
+     hw.acpi.cpu.px_dom1.select: 2600
+     hw.acpi.cpu.px_dom0.available: 2600 1300
+     hw.acpi.cpu.px_dom0.members: cpu0(2600)
+     hw.acpi.cpu.px_dom0.select: 2600
+     hw.acpi.cpu.px_global: 2600
+
+Both, EST and CPU P states sysctl's can be adjusted automatically depending on the system load with
+sysutils/estd from pkgsrc.
+
 ## Backlight 
 
 Switch backlight to (usable) minimum. There might be several ways to do it, you have to find the one which works for you.