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

<snip>

>
> I think the word "Americans" is appropiate there, but I will comment no
> futher.

No such thing is appropriate! It's highly inappropriate, derogatory and
wildly OT, at best. I for one take great offense at the implication.

>
> >>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 know they use less power when idle, but do they use less when taken
> offline with psradm, than when online, but idle?

Check the SparcII operating specs for you procs on whatever the minimal
temperature is, that's probably close to the temp you'd see plus the
ambient heat given off by surrounding circuits. Cross-ref the hard-copy
or online handbooks for the Ultra-80 for other BTU related info.

Alternatively, measure the total BTU output and/or overall room
temperatures a few times with, and then without, the procs and any
additional systems online.

>
> At the moment its inconvenient to locate my temperature sensor on the
> output of the Sun's fans, but I'll get some longer leads on it and try.
>
> >>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
>
> No such luck on the Ultra 80. However, I have can easily measure the
> temperature. At the moment I have only one, but can add another 4, and
> read them via the computer.
>
> > 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.
>
> I care about less than 150ps actually, but that is of the time measured
> by the instrument.
>
> The errors induced in the test equipment will not occur with a change of
> air inlet temperature that occur for 100's of ms or probably seconds.
> Putting the CPUs on/offline will not cause rapid changes in room
> temperature, so timing is not an issue.
>
> Sorting out an algorithm might be.
>
> > 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 :-)

The whole thing sounds a bit susceptible to the Heisenberg Principle in
a macro way Hope you have a descent oscillator in whatever's keeping
those ticks for you.