Most notable have been the extensive SMP
enhancements and work to provide fine-grained multi-threading
in the network stack
. This was spurred, even Linus
admits, in response to the Mindcraft
survey, finding NT
on a multi-CPU machine serving static
content faster/more scalable
As some of the more informed laymen might imagine, this has involved rewriting a fairly significant amount of the kernel, and has been a monumental effort, taking much longer than folks guessed. Of course, the reason why you want to run Linux, faster than NT or not, is because unlike Microsoft, the linux guys won't release it 'till it's finished. It's nice not to have to reboot every day to keep from crashing.
Anecdotally, the enhancements have been extremely effective. Especially anyone with a multi-CPU machine should find the new kernel well worth the time to upgrade.