Avoiding blocking system calls in a user-level thread scheduler for shared memory multiprocessors

Abstract

SMP machines are frequently used to perform heavily parallel computations. The multithreading paradigm has proved suitable for exploiting SMP architectures. In general, application developers use a thread library to write such a program. This library schedules threads itself or relies on the operating system kernel to do so. However, both of these approaches pose a number of problems. This dissertation describes the extension of two existing user-level thread schedulers, one for uniprocessors and one for SMPs. This will enable the execution of blocking system calls without blocking the scheduler kernel. In order to do this we make use of an operating system extension called scheduler activations. The usefulness of avoiding blocking system calls is apparent in server applications that carry out several I/O operations and which need to handle multiple clients simultaneously. A web server that is capable of dispensing static pages and which implements the HTTP 1.0 protocol is also implemented to demonstrate the effectiveness of this approach.