Hmm...typically multi-core scaling issues are in the area of memory contention and cache coherence (and therefore are for the most part not dependent on the OS and its scheduler).
If it is independent of the OS, then how does one go about tuning it.
Consider this - I get a 12 core server on which I want multiple webserver instances + DB. Can one create CPU pools (say core 1,2,3 for webservers, 4,5,6,7 for DB, etc.) ?
I know about taskset, but should one be using it ?
You can do this in some systems (we've done it on solaris systems for example), but realize that for any of the high scale websites, they run dedicated machines for database and web services; and that's essentially a mandatory requirement just for purposes of having visibility into what is affecting your server performance at scale.
It might also be worth mentioning that Facebook doesn't actually run MySQL like you'd get from Oracle; they have their own custom patch set that is tuned specifically for their servers (based on their OS modifications as well). Probably the closest equivalent would be Percona's XtraDB table engine, and I have seen some benchmarks that would certainly show comparable performance at 32 cores if not slightly better, but of course it will be somewhat workload dependent. It's mostly irrelevant though to "internet oriented" companies, very few are looking for 32+ core systems as a solution to their problems.