Hypervisors, popularized by Xen and VMware, are quickly becoming commodity. They are appropriate for many usage scenarios, but there are scenarios that require system virtualization with high degrees of both isolation and efficiency. Examples include HPC clusters, the Grid, hosting centers, and PlanetLab. We present an alternative to hypervisors that is better suited to such scenarios. The approach is a synthesis of prior work on resource containers and security containers applied to general-purpose, time-shared operating systems. Examples of such container-based systems include Solaris 10, Virtuozzo for Linux, and Linux-VServer. As a representative instance of container-based systems, this paper describes the design and implementation of Linux-VServer. In addition, it contrasts the architecture of Linux-VServer with current generations of Xen, and shows how Linux-VServer provides comparable support for isolation and superior system efficiency.

The rapid advancements of networking technology have boosted potential bandwidth to the point that the cabling is no longer the bottleneck. Rather, the bottlenecks lie at the crossing points, the nodes of the network, where data traffic is intercepted or forwarded. As a result, there has been tremendous interest in speeding those nodes, making the equipment run faster by means of specialized chips to handle data trafficking. The Network Processor is the blanket name thrown over such chips in their varied forms. To date, no performance data exist to aid in the decision of what processor architecture to use in next generation network processor. Our goal is to remedy this situation. In this study, we characterize both the application workloads that network processors need to support as well as emerging applications that we anticipate may be supported in the future. Then, we consider the performance of three sample benchmarks drawn from these workloads on several state-of-the-art processor architectures, including: an aggressive, out-of-order, speculative super-scalar processor, a fine-grained multithreaded processor, a single chip multiprocessor, and a simultaneous multithreaded processor (SMT). The network interface environment is simulated in detail, and our results indicate that SMT is the architecture best suited to this environment.

Many modern extensible systems, such as Java and the SPIN operating system, depend on type safety for memory protection. Unfortunately, current type-safe languages do not support systems programming well, because they do not give programmers the ability to deal with untyped data easily. In particular, they do not support the ability to cast between untyped data and language-level types. We describe a powerful, type-safe cast operator that helps programmers write low-level systems codes in type-safe languages. We have implemented this operator in Modula-3 for the SPIN operating system, and we give specific examples of how we use it in SPIN. © 1998 John Wiley & Sons, Ltd.

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.

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 system's 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.

Parallel data flow analysis methods offer the promise of calculating detailed semantic information about a program at compile-time more efficiently than sequential techniques. Previous work on parallel elimination methods (Zobel, 1990) has been hampered by the lack of control over interval size; this can prohibit effective parallel execution of these methods. To overcome this problem, we have designed the region analysis method, a new elimination method for data flow analysis. Region analysis emphasizes flow graph partitioning to enable better load balancing in a more effective parallel algorithm. We present the design of region analysis and the empirical results we have obtained that indicate: the prevalence of large intervals in flow graphs derived from real programs; and the performance improvement of region analysis over parallel Allen-Cocke interval analysis. Our implementation analyzed programs from the Perfect Benchmarks and netlib running on a Sequent Symmetry S81.>