Unbound's performance on multi-core cpu

hi,

I ran unbound in some different servers to get respective performance.

Those servers differentiate mainly on CPU.

I also configure Unbound according to CPU(the number of CPU, the core of earch CPU)

to optimise system (i.e.http://www.unbound.net/documentation/howto_optimise.html).

I get the result that UNbound’s performance is better on 1 cpu with 2-core(intel E3120) than

multi-CPU(2,4) with multi-core(4), suppost all queries get answers from cache.

how to configure unbound to make use of latest CPU(multi-core)?

thank you.