Communication-intensive Parallel Applications Research Articles

On the Benefit of Processor Coallocation in Multicluster Grid Systems

In multicluster grid systems, parallel applications may benefit from processor coallocation, that is, the simultaneous allocation of processors in multiple clusters. Although coallocation allows the allocation of more processors than available in a single cluster, it may severely increase the execution time of applications due to the relatively slow wide-area communication. The aim of this paper is to investigate the benefit of coallocation in multicluster grid systems, despite this drawback. To this end, we have conducted experiments in a real multicluster grid environment, as well as in a simulated environment, and we evaluate the performance of coallocation for various applications that range from computation-intensive to communication-intensive and for various system load settings. In addition, we compare the performance of scheduling policies that are specifically designed for coallocation. We demonstrate that considering latency in the resource selection phase improves the performance of coallocation, especially for communication-intensive parallel applications.

Porting the OPATM-BFM Application to a Grid e-Infrastructure – Optimization of Communication and I/O Patterns

OPATM-BFM is an off-line three-dimensional coupled eco-hydrodynamic simulation model used for biogeochemical and ecosystem-level predictions. This paper presents the first results of research activities devoted to the adaptation of the parallel OPATM- BFM application for an efficient usage in modern Grid-based e-Infrastructures. For the application performance on standard Grid archi- tectures providing generic clusters of workstations, such results are important. We propose a message-passing analysis technique for communication-intensive parallel applications based on a preliminary application run analysis. This technique was successfully used for the OPATM-BFM application and allowed us to identify several optimization proposals for the current realization of the communication pattern. As the suggested improvements are quite generic, they can be potentially useful for other parallel scientific applications.

Supporting parallel applications on clusters of workstations: The Virtual Communication Machine-based architecture

This paper presents a novel networking architecture designed for communication intensive parallel applications running on clusters of workstations (COWs) connected by high speed networks. The architecture addresses what is considered one of the most important problems of cluster-based parallel computing: the inherent inability of scaling the performance of communication software along with the host CPU performance. The Virtual Communication Machine (VCM), resident on the network coprocessor, presents a scalable software solution by providing configurable communication functionality directly accessible at user-level. The VCM architecture is configurable in that it enables the transfer to the VCM of selected communication-related functionality that is traditionally part of the application and/or the host kernel. Such transfers are beneficial when a significant reduction of the host CPU’s load translates into a small increase in the coprocessor’s load. The functionality implemented by the coprocessor is available at the application level as VCM instructions. Host CPU(s) and coprocessor interact through shared memory regions, thereby avoiding expensive CPU context switches. The host kernel is not involved in this interactions it simply “connects” the application to the VCM during the initialization phase and is called infrequently to handle exceptional conditions. Protection is enforced by the VCM based on information supplied by the kernel. The VCM-based communication architecture admits low cost and open implementations, as demonstrated by its current ATM-based implementation based on off-the-shelf hardware components and using standard AAL5 packets. The architecture makes it easy to implement communication software that exhibits negligible overheads on the host CPU(s) and offers latencies and bandwidths close to the hardware limits of the underlying network. These characteristics are due to the VCM’s support for zero-copy messaging with gather/scatter capabilities and the VCM’s direct access to any data structure in an application’s address space. This paper describes two versions of an ATM-based VCM implementation, which differ in the way they use the memory on the network adapter. Their performance under heavy load is compared in the context of a synthetic client/server application. The same application is used to evaluate the scalability of the architecture to multiple VCM-based network interfaces per host. Parallel implementations of the Traveling Salesman Problem and of Georgia Tech Time Warp, an engine for discrete-event simulation, are used to demonstrate VCM functionality and the high performance of its implementation. The distributed- and shared-memory versions of these two applications exhibit comparable performance, despite the significant cost-performance advantage of the distributed-memory platform.

Enhanced PVM communications over a high-speed LAN

Performance results of PVM over a local ATM network show the availability of much greater communication bandwidth over traditional LANs such as Ethernet. Application-level performance, however, still lags far behind the capabilities of the physical medium. Realizing the full potential of high-speed networks, therefore, will require further improvements in both hardware and software components of network I/O subsystems.Emulating a parallel machine via a collection of heterogeneous, independent hosts and a general-purpose local-area network has obvious advantages, including cost-effectiveness and very large aggregate processing power and memory. However, the ability of most general-purpose LANs to support communication-intensive parallel applications is debatable. Today, with the emergence of several high-speed, switch-based networks, such as High-Performance Parallel Interface (Hippi), Fibre Channel, and Asynchronous Transfer Mode (ATM), networks that effectively support communication-intensive parallel applications may soon become a reality.Network-based computing offers several advantages. First, independent, commercially available systems and a general LAN can readily incorporate advances in processor and network technology. Second, due to the large memory and processing power available in the aggregate collection of individual host systems, very large applications can execute on a collection of relatively low-priced host systems. Third, the underlying network can support high-speed input/output to applications, for instance, by using disk arrays.One factor that previously fueled much skepticism about the feasibility of network-based parallel computing was the limitations imposed by using traditional LANs, such as Ethernet, as the system interconnect. For many typical network applications that require only occasional file transfers, or infrequent small amounts of data to be transmitted between workstations, an Ethernet-based cluster of workstations will suffice. However, for network-based applications, such as communication-intensive, course-grain parallel applications, traditional networks such as Ethernet simply cannot provide adequate performance. Thus, for this study, we chose a high-speed transport mode as the supporting communication medium.