Chris Hawblitzel

Low-Latency Communication on the IBM RISC System/6000 SP

The IBM SP is one of the most powerful commercial MPPs, yet, in spite of its fast processors and high network bandwidth, the SPs communication latency is inferior to older machines such as the TMC CM-5 or Meiko CS-2. This paper investigates the use of Active Messages (AM) communication primitives as an alternative to the standard message passing in order to reduce communication overheads and to offer a good building block for higher layers of software. The first part of this paper describes an implementation of Active Messages (SP AM) which is layered directly on top of the SPs network adapter (TB2). With comparable bandwidth, SP AMs low overhead yields a round-trip latency that is 40% lower than IBM MPLs. The second part of the paper demonstrates the power of AM as a communication substrate by layering Split-C as well as MPI over it. Split-C benchmarks are used to compare the SP to other MPPs and show that low message overhead and high throughput compensate for SPs high network latency. The MPI implementation is based on the freely available MPICH version and achieves performance equivalent to IBMs MPI-F on the NAS benchmarks.

J-Kernel: a capability-based operating system for Java

Safe language technology can be used for protection within a single address space. This protection is enforced by the languages type system, which ensures that references to objects cannot be forged. A safe language alone, however, lacks many features taken for granted in more traditional operating systems, such as rights revocation, thread protection, resource management, and support for domain termination. This paper describes the J-Kernel, a portable Java-based protection system that addresses these issues. J-Kernel protection domains can communicate through revocable capabilities, but are prevented from directly sharing unrevocable object references. A number of micro-benchmaxks characterize the costs of language-based protection, and an extensible web and telephony server based on the J-Kernel demonstrates the use of language-based protection in a large application.

Resource management for extensible Internet servers

With the continued spread of the Internet the typical computing model for servers is undergoing a drastic change. In the past, server systems have moved from providing interactive time-sharing service to providing fileserver and now more general back-office (mail, database, web, etc.) services. While the characteristics of the new Internet server systems are not yet clear, we expect that Internet servers will have at least three characteristics that distinguish them drastically from today’s servers: (i) high code mobility, (ii) large numbers of anonymous users, and (iii) significant concern for the efficient use of resources.

Security versus performance tradeoffs in RPC implementations for safe language systems

In current distributed systems, the performance of remote procedure calls (RPCs) is determined primarily by the performance of the underlying network transport. While the overheads of the RPC system itself are secondary, two ongoing developments are likely to change this and will cause the current RPC systems to become the bottleneck in communication: user-level network interfaces and safe languages. User-level network interfaces such as VIA [2], U-Net [10], Fast Messages [8], NoW Active Messages [1], or Shrimp VMMC [3] are removing the operating system from the critical communication path by allowing applications to access the network interface directly. As a result, the overhead of the network transport underlying RPC decreases by almost an order of magnitude. At the same time, the increasing adoption of Java as the “internet programming language” places a heavier burden on the RPC system because communication among Java programs must satisfy the type safety properties assumed by the language run-time (this is a general issue with safe languages). Typically enforcing this type safety requires additional operations (e.g. checks) in the critical RPC path.