1. A system including instructions recorded on a computer-readable medium, the system comprising: a sampler configured to determine a first performance measurement of an executing task, while the task is executed by a first number of nodes operating in parallel, and configured to determine a second performance measurement of the executing task, while the task is being executed by a second number of nodes operating in parallel; and a calibrator configured to calculate an overhead factor characterizing a change of a parallelism overhead of executing the task with nodes executing in parallel, relative to a change in a number of the nodes, based on the first performance measurement and the second performance measurement, and configured to determine an optimal number of nodes to operate in parallel to continue executing the task, based on the overhead factor.