[Soekris] Idle temperature under various operating systems

[Martin Johnson]

On 18 Aug 2007, at 15:31, RB wrote:

> I've noticed something with my 4501s (and with other x86 hardware, for
> that matter), that I find a matter of curiosity.
>
> When running FreeBSD (m0n0wall or it's derivative pfSense), my
> machines are palpably warm, even when completely idle.  I've not taken
> any temperature readings, but one can hold their hand over the naked
> board and feel heat radiating off, and the metal cases they're in are
> warm to the touch.
>
> However, under Linux (OpenWRT, GNAP) when the machines are idle,
> they're completely cool - can't feel [much] warmth, and the cases are
> always cool to the touch.  If I run a CPU soaker, then they warm up to
> temperatures similar to what the ones running FreeBSD reach at idle.
> Does the FBSD kernel have a busy-wait, or does it not do no-ops,
> or...?  Without doing any scientific testing, I can say that they're
> both responsive and seem to perform similarly under the moderate (home
> router) loads I put on them.
>
> Any insight?

I'm guessing the thermal behaviour you're seeing reflects the  
firewall application you're running, not the OS.

pfSense (and presumably m0n0Wall) contain lots of stats-gathering  
code in order to facilitate the pretty RRD graphs.  So there is  
always some background CPU load.  On my 4801 it seems to hover around  
7% with modest traffic, but it peaks much higher, and displaying the  
RRD graphs maxes it out.

The 4501 is half the speed of the 4801, so I'd expect it to work a  
bit harder.  What percentage CPU usage are you seeing in the GUI?

Do you get CPU temperature display on the 4501 in pfSense?   My 4801  
normally shows around 55 centigrade in pfSense, and the ambient temp  
in the room is about 17 centigrade.

As an experiment, I then nailed the CPU up to 100% by SSHing into the  
box and running
	while (1)
	echo -n ;
	end

The system remained responsive. After 20 minutes, pfSense showed the  
CPU temp to be 63 centigrade, but it didn't climb any higher.

Hope this helps,

- Martin