Using interpreted CompositeCalls to improve operating system services

A large number of protection domain crossings and context switches is often the cause of bad performance in complex object-oriented systems. We have identified the CompositeCall pattern which has been used to address this problem for decades. The pattern modifies the traditional client/server interaction model so that clients are able to build compound requests that are evaluated in the server domain. We implemented CompositeCalls for both a traditional OS, Linux, and an experimental object-oriented μkernel, Off++. In the first case, we learned about implications of applying CompositeCall to a non-object-oriented `legacy' system. In both experiments, we learned when CompositeCalls help improving system performance and when they do not help. In addition, our experiments gave us important insights about some pernicious design traditions extensively used in OS construction.