Przemyslaw Pardyak

Extensibility safety and performance in the SPIN operating system

This paper describes the motivation, architecture and performance of SPIN, an extensible operating system. SPIN provides an extension infrastructure, together with a core set of extensible services, that allow applications to safely change the operating systems interface and implementation. Extensions allow an application to specialize the underlying operating system in order to achieve a particular level of performance and functionality. SPIN uses language and link-time mechanisms to inexpensively export fine-grained interfaces to operating system services. Extensions are written in a type safe language, and are dynamically linked into the operating system kernel. This approach offers extensions rapid access to system services, while protecting the operating system code executing within the kernel address space. SPIN and its extensions are written in Modula-3 and run on DEC Alpha workstations.

SPIN —an extensible microkernel for application-specific operating system services

Application domains such as multimedia, databases, and parallel computing, require operating system services with high performance and high functionality. Existing operating systems provide fixed interfaces and implementations to system services and resources. This makes them inappropriate for applications whose resource demands and usage patterns are poorly matched by the services provided. The SPIN operating system enables system services to be defined in an application-specific fashion through an extensible microkernel. It offers applications fine-grained control over a machines logical and physical resources through run-time adaptation of the system to application requirements.

SPIN: an extensible microkernel for application-specific operating system services

Application domains such as multimedia, databases, and parallel computing, require operating system services with high performance and high functionality. Existing operating systems provide fixed interfaces and implementations to system services and resources. This makes them inappropriate for applications whose resource demands and usage patterns are poorly matched by the services provided. The SPIN operating system enables system services to be defined in an application-specific fashion through an extensible microkernel. It offers applications fine-grained control over a machines logical and physical resources through run-time adaptation of the system to application requirements.

Protection is a software issue

Modern operating systems are strongly dependent on software mechanisms to protect system resources from users. This is true despite the fact that the promoters of these systems imply that their reliability and integrity derive solely from the use of a core set of protected hardware mechanisms, such as address spaces and protected supervisor mode. While typical microprocessors provide cheap and effective hardware mechanisms to protect the load word/store word interface, operating systems are forced to abstract and virtualize this interface to export a far richer set, of resources such as files, sockets, threads, and consoles. The access semantics for these resources are almost always protected by software checks and not hardware. Processor architectures simply do not provide enough fine-grained control over access to shared system resources to ensure that a program only accesses the resources to which it is allowed. Our position is that software protection mechanisms are not only necessary, but have inherent advantages over hardware for enforcing the protection requirements of an operating system. Software is flexible, explicit, precise, and in many cases, open to incredible optimizations. By contrast, hardware mechanisms are rigid, implicit, imprecise, and unoptimizable.

A memory-efficient real-time non-copying garbage collector

Garbage collectors used in embedded systems such as Personal Java and Inferno or in operating systems such as SPIN must operate with limited resources and minimize their impact on application performance. Consequently, they must maintain short real-time pauses, low overhead, and a small memory footprint. Most garbage collectors, including the Treadmill algorithm, are inadequate because they sacrifice space for time. We have implemented a new Treadmill variant that provides good memory utilization by using real-time page-level management techniques that reduce fragmentation. A page-wise collection is used to locate pages of free memory, which are then dynamically reassigned between free lists as needed. Virtual memory is used to dynamically remap free pages into continuous ranges, and objects are allocated from under-utilized pages when needed. Finally, the use of header compaction and arbitrary free-list sizes reduces internal fragmentation. Our experiments demonstrate that we have substantially improved memory utilization without compromising latency or overhead, and that the new collector performs very well for SPINs workloads and regular Modula-3 programs.

A group structuring mechanism for a distributed object-oriented language

Describes a structuring mechanism for grouping objects in a distributed object-oriented language. A group structuring mechanism provides a single flexible method for managing distributed applications that involve complicated communication protocols and sophisticated structure. We have added such a mechanism to the Emerald distributed object-oriented language and its run-time system. Our group structuring mechanism fits entirely within the context of object-oriented programming, so similar mechanisms could be added to other distributed object-oriented languages.<<ETX>>