If you're getting a 4x difference in IPC using a crypto microbenchmark from compiled C code (i.e. it doesn't sound like you're bandwidth or I/O limited), there has to be something else at work. POWER8 is a nice core, but it's not that wide. Maybe the compiler was recognizing your operations and replacing them with AES primitives?
Yes, but at this kind of multiplier only in the case where the entire test is 100% cache-resident on one CPU and spilling on the other. Crypto stuff tends to have small working sets, so my intuition is that it's got to be something else.
