Philippe Bernadat

Towards a distributed platform for resource-constrained devices

Many visions of the future predict a world with pervasive computing, where computing services and resources permeate the environment. In these visions, people will want to execute a service on any available device without worrying about whether the service has been tailored for the device. We believe that it will be difficult to create services that can execute well on the wide variety of devices that are being developed because of problems with diversity and resource constraints. We believe that these problems can be greatly reduced by using an ad-hoc distributed platform to transparently off-load portions of a service from a resource-constrained device to a nearby server. We implemented a preliminary prototype and emulator to study this approach. Our experiments show the beneficial use of nearby resources to relieve both memory and processing constraints, when it is appropriate to do so. We believe that this approach will reduce the burden on developers by masking more device details.

Susceptibility of commodity systems and software to memory soft errors

It is widely understood that most system downtime is accounted for by programming errors and administration time. However, a growing body of work has indicated an increasing cause of downtime may stem from transient errors in computer system hardware due to external factors, such as cosmic rays. This work indicates that moving to denser semiconductor technologies at lower voltages has the potential to increase these transient errors. In this paper, we investigate the susceptibility of commodity operating systems and applications on commodity PC processors to these soft-errors and we introduce ideas regarding the improved recovery from these transient errors in software. Our results indicate that, for the Linux kernel and a Java virtual machine running sample workloads, many errors are not activated, mostly due to overwriting. In addition, given current and upcoming microprocessor support, our results indicate that those errors activated, which would normally lead to system reboot, need not be fatal to the system if software knowledge is used for simple software recovery. Together, they indicate the benefits of simple memory soft error recovery handling in commodity processors and software.

Psi-Pervasive Services Infrastructure

Future systems have been characterized as ubiquitous, pervasive, and invisible. They will consist of devices that are diverse in size, performance, and power consumption. Some of these devices will be mobile, posing additional requirements to system software and applications. The focus will move from technology to deployment and ease of use of services. Consequently, traditional paradigms for reasoning about, designing, and implementing software systems and services will no longer be sufficient. We believe that this future vision will rely on a three-tier infrastructure consisting of back-end servers, infrastructure servers, and front-end clients (mobile or static, handheld or embedded). The critical question for future systems will be how to deliver services on demand from back-end servers to resource-constrained clients. If we can handle the new requirements of these systems, we can enable this computing infrastructure to offer significantly more services to users in a more pervasive way.

Case Studies in Security and Resource Management for Mobile Object Systems

Mobile objects have gained a lot of attention in research and industry in the recent past, but they also have a long history. Security is one of the key requirements of mobile objects, and one of the most researched characteristics related to mobility. Resource management has been somewhat neglected in the past, but it is being increasingly addressed, in both the context of security and QoS. In this paper we place a few systems supporting mobile objects in perspective based upon how they address security and resource management. We start with the theoretical model of Actors that supports concurrent mobile objects in a programming environment. Then we describe task migration for the Mach microkernel, a case of mobile objects supported by an operating system. Using the OMG MASIF standard as an example, we then analyze middleware support for mobile objects. Mobile Objects and Agents (MOA) system, is an example of middleware level support based on Java. The active networks project, Conversant, supports object mobility at the communication protocol level. We summarize these projects, comparing their security and resource management, and conclude by deriving a few general observations on how security and resource management have been applied and how they might evolve in the future.

Building middleware for real-time dependable distributed services

We consider a real-time, distributed service to be dependable if it continues to have timely, predictable behavior even in the presence of partial failures. Services with this property are desirable in a host of real-time scenarios, including factory floor automation, medical monitoring equipment, and combat systems. Most distributed services built with contemporary fault-tolerance toolkits are not dependable; they exhibit unpredictable, albeit logically correct, behavioral patterns under failure conditions. We have designed and implemented middleware explicitly for real-time dependable services. We aimed at maintaining sub-second worst-case guarantees for failure detection and recovery, even when failures conspire with network load and CPU load to undermine determinism. The paper reports our experience in marrying software fault tolerance and real-time disciplines, from the definition of the requirements to the characterization of the resulting system.