We introduce a new performance metric, called Load Balancing Factor (LBF), to evaluate different tuning alternatives of workload migration within a distributed/parallel program. The metric is unique because it shows the performance implications of a specific tuning alternative rather than quantifying where time is spent in the program. Previously we developed a variation of the metric for coarse-grained process placement, and demonstrated that it accurately predicts the placement impact. In this paper we focus on a variation designed for fine-grained function shipping in a client/server environment and present its online algorithm. We use a synthetic application to show that LBF provides accurate guidance about procedure-level migration. (UMIACS-TR-2002-55)