[hollerith]

Up to 20% slower than what?

(Than SMP systems, I guess, but the OP does not say.)

[rys]

Than keeping memory accesses chip local (I guess via thread pinning). The comparison was done on the same hardware platform.

[CJefferson]

I am not surprised, I have seen slowdowns of 40%. NUMA leads to an annoying bimodal timing, where some runs are fast and others slow.