There is some limited support for power management in OpenSolaris 2008.05, but by default it is not enabled (hopefully that will change in a future release). There is an entry on the BigAdmin wiki page that describes the supported CPUs (from both Intel and AMD) and the simple steps for modifying the /etc/power.conf file. But this blog entry from Mark Haywood provides quite a bit more information. In it, he describes the CPU frequency scaling feature in detail. The feature slows the CPU when idle, so that the chip uses less power and generates less heat.
To follow his instructions, all I had to do was enter this at a command line:
$ pfexec gedit /etc/power.conf
I added two lines to the end of /etc/power.conf:
Saved the file and then ran this command:
And now OpenSolaris 2008.05 is happily slowing down my CPU when it is idle.