Second CPU missing of Dual Core

The current Nvidia driver (the one from Nvidia itself "NVIDIA-Linux-x86_64-260.19.21") leads to those problems. After uninstalling it and installing the one of Ubuntu again the second CPU shows up again. Not sure why that driver has this problem, but I will test things a bit further when I have the time.

I noticed that I had this problem right after I performed

    sudo pm-powersave true

I inverted it, restarted, and my laptop now recognizes my 2 cpus. (For completeness...)

   sudo pm-powersave false

I performed this on:

MacbookPro 5,2

Ubuntu 12.04 LTS

Intel Core 2 Duo

I also experienced the problem of the missing cpu with a Core 2 Duo Asus N90S notebook and Ubuntu 10.10. Also, the system would only boot the LiveCD and finished installation with "nolapic" in the kernel params. Under 9.10 the system behaved normally.

Under 10.10, removing the NVidia driver did not fix the missing cpu for me and isn't the only problem.

After reading some other cases of this I had a feeling a kernel compile was in order.

I grabbed the official ubuntu linux kernel source module and compiled a new kernel, with the correct CPU type selected, Power Management disabled and CPU_HOTPLUG disabled. Installing that kernel brought back the second cpu, and ability to correctly boot up without the special "nolapic" setting.

I'm posting this in the hopes it will be useful to other people having problems.