Comment 16 for bug 75174

A really quick workaround is to issue:

sudo killall klogd

This will stop the hard drive grinding (if you experience that), but that still doesn't fix the infinite loop (most likely) in kacpi_notify which hogs a lot of CPU power. You can renice it to priority 19 to make it not as bad.

If you don't mind recompiling your kernel, you can go to drivers/acpi/thermal.c, find this:

static void acpi_thermal_check(void *data)
{

and add right after it:

printk(KERN_WARNING PREFIX "Bypassing acpi_thermal_check\n");
return;
...

This will disable thermal checking, meaning the fan won't come on when the processor gets busy (don't blame me if your CPU overheats, which it probably won't). I did this myself, and it got rid of the kacpi_notify thrashing completely.

If you're a kernel developer, see if you can find the infinite loop in acpi_thermal_check :)