This paper presents Capriccio, a scalable thread package for use with high-concurrency servers. While recent work has advocated event-based systems, we believe that threadbased systems can provide a simpler programming model that achieves equivalent or superior performance.

This white paper describes Scout, a new operating system being designed for systems connected to the National Information Infrastructure (NII). Scout provides a communication-oriented software architecture for building operating system code that is specialized for the different systems that we expect to be available on the NII. It includes an explicit path abstraction that both facilitates effective resource management and permits optimizations of the critical path that I/O data follows. These path-enabled optimizations, along with the application of advanced compiler techniques, result in a system that has both predictable and scalable performance. June 17, 1994 Department of Computer Science The University of Arizona Tucson, AZ 1 Introduction As the National Information Infrastructure (NII) evolves, and digital computer networks become ubiquitous, communication will play an increasingly important role in computer systems. In fact, a recent report on the NII rejects the term "compu...

Dynamic code generation allows specialized code sequences to be crafted using runtime information. Since this information is by definition not available statically, the use of dynamic code generation can achieve performance inherently beyond that of static code generation. Previous attempts to support dynamic code generation have been low-level, expensive, or machine-dependent. Despite the growing use of dynamic code generation, no mainstream language provides flexible, portable, and efficient support for it.

Modern commodity operating systems are large and complex systems developed over many years by large teams of programmers, containing hundreds of thousands of lines of code. Consequently, it is extremely difficult to add significant new functionality to these systems. In response to this problem, a number of recent research projects have explored novel operating system architectures to support untrusted extensions, including SPIN, VINO, Exokernel, and Fluke. Unfortunately, these architectures require substantialimplementation effort and are not generally available in commodity systems. In contrast, by leveraging the technique of interposition, we have designed and implemented a prototype extension system called SLIC which requires only trivial operating system

The defining tragedy of the operating systems community has been the definition of an operating system as software that both multiplexes and abstracts the hardware is based on the assumption that it is possible both to define abstractions that are appropriate for all areas and to implement them to perform efficiently in all situations. We believe that the fallacy of this quixotic goal is self-evident, and that the operating system problems of the last two decades (poor performance, poor reliability, poor adaptability, and in exibility) can be traced back to it. The solution we propose is simple: complete elimination of operating system abstractions by lowering the operating system interface to the hardware level.

A number of interacting trends in operating system structure, processor architecture, and memory systems are increasing both the rate of translation lookaside buffer (TLB) misses and the cost of servicing a miss. This paper presents two novel software schemes, implemented under Mach 3.0, to decrease both the number and the cost of kernel TLB misses (i.e., misses on kernel data structures, including user page tables). The first scheme is a new use of prefetching for TLB entries on the IPC path, and the second scheme is a new use of software caching of TLB entries for hierarchical page table organizations. For a range of applications, prefetching decreases the number of kernel TLB misses by 40% to 50%, and caching decreases TLB penalties by providing a fast path for over 90% of the misses. Our caching scheme also decreases the number of nested TLB traps due to the page table hierarchy, reducing the number of kernel TLB miss traps for applications by 20% to 40%. Prefetching and caching, ...

New distributed computing applications are driving the development of more specialized protocols, as well as demanding greater control over the communication substrate. Here, a network subsystem that supports modular, finegrained construction of high-level protocols such as atomic multicast and group RPC is described. The approach is based on extending the standard hierarchical model of the x-kernel with composite protocols in which micro-protocol objects are composed within a standard runtime framework. Each micro-protocol realizes a separate semantic property, leading to a highly modular and configurable implementation. In contrast with similar systems, this approach provides finer granularity and more flexible inter-object communication. The design and prototype implementation runing on Mach are described. Performance results are also given for a micro-protocol suite implementing variants of group RPC. 1 Introduction Network protocols that are implemented at high levels of the pro...

To provide modularity and performance, operating system kernels should have only minimal embedded functionality. Today's operating systems are large, inefficient and, most importantly, inflexible. In our view, most operating system performance and flexibility problems can be eliminated simply by pushing the operating system interface lower. Our goal is to put abstractions traditionally implemented by the kernel out into user-space, where user-level libraries and servers abstract the exposed hardware resources. To achieve this goal, we have defined a new operating system structure, exokernel, that safely exports the resources defined by the underlying hardware. To enable applications to benefit from full hardware functionality and performance, they are allowed to download additions to the supervisor-mode execution environment. To guarantee that these extensions are safe, techniques such as code inspection, inlined cross-domain procedure calls, and secure languages are used. To test and ...

Virtual memory (VM) is a notoriously complicated abstraction to implement, and is hard to change, specialize, or replace. Although a certain degree of flexibility is achieved by user-level pagers, the control they provide is limited: they leave much of the VM system fixed in the kernel, unreachable by the application. As applications become more diverse and the opportunity cost of bad memory policies grows, it is essential for applications to have more control over the VM abstraction. In this position paper, we motivate and describe a VM system that is implemented completely at the application level. To the best of our knowlege this system is the first complete example of application-level virtual memory (AVM). AVM allows applications to easily specialize, modify, or even replace the VM abstractions offered. For example, on architectures with software TLB management, applications can even select their own page-table structures. In addition, AVM simplifies the OS kernel, since the kerne...

In 1981, Stonebraker wrote: Operating system services in many existing systems are either too slow or inappropriate. Current DBMSs usually provide their own and make little or no use of those o ered by the operating system. [STON81] The standard operating system model has changed little since that time, and we believe that, at its core, it is the wrong model for DBMS and other resource-intensive applications. The standard model is in exible, uncooperative, and irregular in its treatment of resources. We describe the design of a new system, the VINO kernel, which addresses the limitations of standard operating systems. It focuses on three key ideas: Applications direct policy. Kernel mechanisms are reusable by applications. All resources share a common extensible interface. VINO's power and exibility make it an ideal platform for the design and implementation of traditional and modern database management systems. 1