It was really a very interesting read for me today about the article - SMP alternatives. This seems to be a very old artcile, but I found this to be a most stumbledupon article pertain to linux kernel (Yep, was browsing the top links at StumbleUpon in the kernel category).
This article explains that concept of "alternatives" in the linux kernel where the kernel can optimize itself during boot time by detecting the number of CPUs present onboard. This is to address the issue where the kernels which are compiled for say 1 CPU would still be using only 1 CPU even after upgrading your hardware to two or more CPUs.
The concept is really interesting and as the article concludes, using "Alternatives" you can always have one single kernel which can adapt and change its run time code to utilize all the CPUs.
One possible use for this, the article says, is in virtual machines where adding or removing of CPUs during runtime is quite probable.
I found the comments for this new article to be as interesting as the article itself.