On 31 Oct 2012 at 6:31, Phil Pokorny wrote: > > On Tue, Oct 30, 2012 at 5:32 PM, Guenter Roeck <linux@xxxxxxxxxxxx> wrote: [...] > > I think that is pretty normal. Keep in mind this is the > > temperature within the chip core, not at the external package. > > And there is internal thermal paste inside the CPU package between the > CPU die itself and the integrated heat spreader. That thermal material > also explains why the silicon die temperature can jump so quickly. It > has a higher deg C/W than the IHS and the heatsink on top of that. > > Phil P. Hmm. Okay - I should check my thermocoupling again. The CPU that "jumps up 30*C in a second" (and jumps down equally fast when I turn the load off) is actually a mobile/embedded version, i.e. it has no I.H.S. The chip is supposedly thermocoupled straight flat to the heatsink. This is a passive heatsink, and it's pretty massive, and I know that heatsinks tend to have quite some thermal inertia. Theoretically this should be the optimum style of thermocoupling in "passive cooled" computers. The catch is, that this particular hardware setup had flawed thermocoupling between the CPU and the heatsink (ex works). The CPU had a pad of "thermocouple chewing gum" on it (likely Fuji Sarcon), approx. 1.1 mm thick. That way the CPU reported 80*C in the BIOS Setup a few dozen seconds after power-up :-) = one core running in a tight loop, other cores asleep, heatsink at 20*C, with the whole computer consuming roughly 27 Watts. (Under Linux, when properly idling, consumption dropped to 12 Watts.) I've tried to fix the problem by inserting a sheet of 1mm copper (about 4 by 4 cm) and by glueing it all toghether by Ceramique CMQ2 - I couldn't use the Coollaboratory liquid (Ga+In+Sn), because the heatsink is made of Aluminium... In a similar scenario, I used to get maybe 10*C of a temperature gradient between a Core2 Duo and the heatsink, and that was across a rather long aluminium "thermocouple bridge". In the case at hand I was fairly satisfied with the way the CPU leans against my improvised heat spreader - I could feel it by the screwdriver, as I was tightening the mounting bolts. Also, the square of the SandyBridge chip is *big* compared to C2D Mobile = more heat transfer surface for a similar wattage. Unfortunately there's no way for me to inspect the gap with the heatsink mounted, so I'll probably have to trust the thermal sensor :-) I still plan to keep an eye on the mobile SandyBridge CPU's whenever I get a chance, to get some "benchmark" / comparable readings on other hardware. I don't meet too many SandyBridge CPU's in our embedded computers - the boxes are dominated by the Atom and I have to agree that even mobile SandyBridge is thermally a bit of an overkill in those small boxes (just like the mobile C2D was). Besides, SandyBridge is stil a bit of a newcomer in the industrial/embedded hardware. There are some SandyBridge notebooks around - so I'll probably have to ask my boss to let me PXE-boot into Linux to run a comparison test on his gear... I can see a similar jump (20-25*C) in a Core i5 Arrandale -based notebook, where I have reasons to believe that the thermocoupling is done right. Hmm... interesting stuff :-) Thanks for your insight - to everybody who responded. Frank Rysanek _______________________________________________ lm-sensors mailing list lm-sensors@xxxxxxxxxxxxxx http://lists.lm-sensors.org/mailman/listinfo/lm-sensors
