Reducing Waiting Costs in User-Level Communication

This paper describes a mechanism for reducing the cost of waiting for messages in architectures that allow userlevel communication libraries. We reduce waiting costs in two ways: by reducing the cost of servicing interrupts, and by carefully controlling when the system uses interrupts and when it uses polling. We have implemented our mechanism on the SHRIMP multicomputer and integrated it with our user-level sockets library. Experiments show that a hybrid spin-then-block strategy offers good performance in a wide variety of situations, and that speeding up the interrupt path significantly improves performance.