David B. Golub

The duality of memory and communication in the implementation of a multiprocessor operating system

Mach is a multiprocessor operating system being implemented at Carnegie-Mellon University. An important component of the Mach design is the use of memory objects which can be managed either by the kernel or by user programs through a message interface. This feature allows applications such as transaction management systems to participate in decisions regarding secondary storage management and page replacement. This paper explores the goals, design and implementation of Mach and its external memory management facility. The relationship between memory and communication in Mach is examined as it relates to overall performance, applicability of Mach to new multiprocessor architectures, and the structure of application programs.

Mach: a system software kernel

The Mach operating system can be used as a system software kernel which can support a variety of operating system environments. Key elements of the Mach design which allow it to efficiently support system software include integrated virtual memory management and interprocess communication, multiple threads of control within on address space, support for transparent system trap callout, and an object programming facility integrated with the Mach IPC mechanisms.<<ETX>>

Translation lookaside buffer consistency: a software approach

We discuss the translation lookaside buffer (TLB) consistency problem for multiprocessors, and introduce the Mach shootdown algorithm for maintaining TLB consistency in software. This algorithm has been implemented on several multiprocessors, and is in regular production use. Performance evaluations establish the basic costs of the algorithm and show that it has minimal impact on application performance. As a result, TLB consistency does not pose an insurmountable obstacle to multiprocessors with several hundred processors. We also discuss hardware support options for TLB consistency ranging from a minor interrupt structure modification to complete hardware implementations. Features are identified in current hardware that compound the TLB consistency problem; removal or correction of these features can simplify and/or reduce the overhead of maintaining TLB consistency in software.

Mach: a foundation for open systems (operating systems)

An alternative approach to building an entire operating system (OS) separating those parts of the OS that control the basic hardware resources (the kernel) from those that determine the unique characteristics of an OS environment, is examined, taking the Mach kernel as an example. Mach features which support OS emulation are discussed. In-kernel and out-of-kernel emulation are described. Two instances of the latter approach, the multithreaded Unix server and the multiserver Unix, are considered. Related work and Mach availability are addressed.<<ETX>>