Why is my Xen DomU kernel using more power/heat when there is no work compared to the default kernel?

Question

I have a special server that is going to be used for graphics processing. It has multiple ATI Radeon GPU cards inside it.

Now when I install Ubuntu server straight from CD it runs relatively cool. There is no graphics, it's just the console.

Now I've compiled a DomU kernel and after I start the machine with that kernel the machine fans start spinning up (where they were nearly silent previously) and the machine is running significantly hotter. In fact it's heating up my little room here like a fan heater!

Is there a setting in the Linux kernel source that could be causing this? Much heat seems to be coming from the graphics cards.

Answer 1

There is a lot more going on when you've got a VM running idle, as opposed to a system that isn't running a VM. On the other hand, it shouldn't be doing enough to heat up your "little room" (personal server?) significantly, and that heat certainly shouldn't be coming from the graphics cards.

My guess is that you've screwed up the kernel config in your custom build and it's disabled something that was probably quite important to your thermal management, but without knowing what you did, it's hard to point to a cause (there are hundreds of settings that could potentially contribute to this). Don't build kernels unless you know what you're doing; distro builds are almost always going to end up better than yours.

Answer 2

I've discovered that this has something to do with the 2.6.39.4 and (possibly) starting it as a console (ubuntu server has no X11).

Even when grabbing the latest natty kernel: http://kernel.ubuntu.com/~kernel-ppa/mainline/v2.6.39-rc4-natty/

and not rolling my own. I get this problem.

I'm going to try a different kernel and see what happens.