Personal Bytes

Attention lads! Ubuntu installs an i386 general kernel by default, ignoring the fact that the CPU may have two cores. So, if you have a dual core processor, say AMD Athlon64 X2, your Linux kernel may well be not detecting the presence of both cores.

Actually, the behaviour of Ubuntu i386 and several other distros is to install a Linux kernel compiled for i368. This covers a lot of old processors, guaranteeing that all work correctly. If you happen to have a better CPU (anything better than a Pentium Pro) then you may not be using the correct kernel with the optimized extensions.

Fortunately, installing a kernel on Ubuntu (or any Debian based distro) is a matter of $ apt-get install kernel-xxx so that won’t represent a problem. The hard stuff is figuring out which kernels fits you better.

So, depending on what you have, this is what you have to do:

• Prior to Pentium Pro: $ apt-get install linux-386
• PPro/Celeron/PII/PIII/PIV: $ apt-get install linux-686
• AMD K7/Athlon/XP: $ apt-get install linux-k7
• Intel PPro/Celeron/PII/PIII/PIV SMP or Double-Core: $ apt-get install linux-686-smp
• AMD Dual-Core/SMP: I have some doubts here. Some have stated that linux-k7-smp isn’t optimized for this models (k8, by the way), so I should install linux-686-smp. But on the other hand, linux-686-* does not have support for 3DNow instructions (to name some). I’ve installed both ($ apt-get install linux-686-smp linux-k7-smp) and I’ve been testing them. If you know something about this, please let me know.

And you can try several kernels, since installing a new one won’t delete the others. Ubuntu automatically adds a new entry in your GRUB so you can choose them prior to booting. If something fails, just pick the old kernel.

Anyway, the difference between linux-386 and linux-*-smp was notorious on my system. You can check out if your system is detecting both cores correctly by doing cat /proc/cpuinfo or by calling top and hitting ‘1′.