Dear Istvan, Is it possible that the communication takes most of the time? For example, if you use GP and the individuals start to bloat, it may happen that the evaluation proceeds slower and slower. Have you tried setting eval.masterproblem.max-jobs-per-slave to smaller values (say 5)? What other parameters are you using? (I am curious about the population size for example). I am attaching a relatively newer version of the master-slave evaluator (it's relatively poorly commented for now, for which I apologize). It also has three apps demo-ing how to do the setup. Best regards, Liviu.