Hi David,

On Sat, 18 Jun 2005 20:52:30 +0100
Dave <nospam@nowhere.com> wrote:

> I'm wondering if I can use my Sun as a computer controlled heater, to
> stabilise the temperature! Using as heating elements the 4 CPUs, and
> adjusting the heat they produce by the amount of work they do, and/or
> taking them offline. (I bet you have not known of an idiot trying that
> one!!!)

You're like my son, always using things for purposes they were not
intended for. I'm trying to console myself with the idea he might be
the guy to solve the world's energy problems.

> Would taking the CPUs offline make them produce less heat or not? I know
> when the Sun is doing a lot of CPU intensive stuff, it certainly runs
> warmer.

Yes. CPUs use less power when they idle. To be absolutely sure, use
prtdiag to see if the temperature of the CPU drops when you take it
off line (do you get CPU temperature readings on a U80, on a Blade2000
it shows both the fan speed and the temperature of both CPUs).

> I'm wondering if I can get the Sun to do more/less work, to help
> stabilise the temperature.

You can parse the prtdiag output for the ambient temperature (which is
more or less related to the room temperature) and stop or start a few
CPU-intensive programs or take CPUs off-line as required.

$ prtdiag -v | grep Ambient
+em-board/cpu0 Ambient 27C -10C 0C 40C 60C okay
+em-board/cpu1 Ambient 26C -10C 0C 40C 60C okay

You'd need to write a little daemon to do the parsing and job/CPU
control as cron's resolution seems far too coarse (you care about
150ps, after all). pbind can be used to bind a process to a CPU,
allowing you to control which CPU is loaded.

Whether this would have any effect on the room temperature remains to
be seen, but it sounds like a fun way to waste some time if you've
got time to waste :-)

--
Stefaan
--
As complexity rises, precise statements lose meaning,
and meaningful statements lose precision. -- Lotfi Zadeh