Coscheduled distributed-Web servers on system area network

As cluster-based Web servers are increasingly adopted to host a variety of network-based services, improving the performance of such servers has become critical to satisfy the customers' demands. Especially, the user response time is an important factor so that clients feel satisfied with the Web services. In this paper, we investigate the feasibility of minimizing the response time of a server by exploiting the advantages of both user-level communication and coscheduling. We, thus, propose a coscheduled server model based on the recently proposed distributed PRESS Web server, where the remote cache accesses can be coscheduled on different nodes to reduce the response time. We experiment this concept using two known coscheduling techniques, called dynamic coscheduling (DCS) and DCS with immediate blocking. We have developed a comprehensive simulation testbed that captures the underlying communication layer in a cluster, the characteristics of various coscheduling algorithms, and the characteristics of the distributed server model to estimate the average delay and throughput with different system configurations. The accuracy of the VIA communication layer and the DCS mechanism is verified using measurements on a 16-node Linux cluster. Extensive simulation of four server models (PRESS over VIA, coscheduled PRESS model with DCS, with DCS and blocking, and Adaptive) using 32-node cluster configurations indicates that the average response time of a distributed server can be minimized significantly by coscheduling the communicating processes. The use of the DCS scheme reduced the average latency up to four times to the PRESS over VIA model that uses only user-level communication.