Is it possible to disable a CPU, not a core? I want to do a test to verify if the performance could make a big difference or not.
I'm using Ubuntu 10.10.
Besides doing this in your BIOS grub has an option called maxcpus.
You can edit this option in when selecting your grub boot option by adding maxcpus=1 to the parameters. Random grub picture:
Choose 'e' and you get to a command line where you can add options.
You can also create permanent boot option in grub by making a copy of your current boot option and add maxcpus=1 to the boot parameters. You can name this 'Ubuntu, kernel 2.5.12-9-386 (1 cpu)' and have it amongst the other boot options like the picture shows.
You can verify running on 1 cpu by issuing:
cat /proc/cpuinfo | grep processor this should show something like this:
processor : 0
processor : 1
And the 2nd line should disappear after booting with 1 CPU.
