Gyu Sang Choi

Coscheduling in Clusters: Is It a Viable Alternative?

In this paper, we conduct an in-depth evaluation of a broad spectrum of scheduling alternatives for clusters. These include the widely used batch scheduling, local scheduling, gang scheduling, all prior communication-driven coscheduling algorithms (Dynamic Coscheduling (DCS), Spin Block (SB), Periodic Boost (PB), and Co-ordinated Coscheduling (CC)) and a newly proposed HYBRID coscheduling algorithm on a 16-node, Myrinet-connected Linux cluster. Performance and energy measurements using several NAS, LLNL and ANL benchmarks on the Linux cluster provide several interesting conclusions. First, although batch scheduling is currently used in most clusters, all blocking-based coscheduling techniques such as SB, CC and HYBRID and the gang scheduling can provide much better performance even in a dedicated cluster platform. Second, in contrast to some of the prior studies, we observe that blocking-based schemes like SB and HYBRID can provide better performance than spin-based techniques like PB on a Linux platform. Third, the proposed HYBRID scheduling provides the best performance-energy behavior and can be implemented on any cluster with little effort. All these results suggest that blocking-based coscheduling techniques are viable candidates to be used in clusters for significant performance-energy benefits.

Co-ordinated coscheduling in time-sharing clusters through a generic framework

In this paper, we attempt to address several key issues in designing coscheduling algorithms for clusters. First, we propose a generic framework for deploying coscheduling techniques by providing a reusable and dynamically loadable kernel module. Second, we implement all prior dynamic coscheduling algorithms (dynamic coscheduling (DCS), spin block (SB) and periodic boost (PB)) and a new coscheduling technique, called co-ordinated coscheduling (CC), using the above framework. Third, with exhaustive experimentation using mixed workloads, we observe that unlike PB, which provided the best performance on a Solaris platform (followed by SB and DCS), the proposed CC scheme outperforms all other techniques on a Linux platform, followed by SB, PB and DCS, in that order. Finally, we argue that due to its modular design, portable implementation on a standard platform, high performance and tolerance to workload mixes, the proposed CC scheme can be a viable scheduling option for time-sharing clusters.

A multi-threaded PIPELINED Web server architecture for SMP/SoC machines

Design of high performance Web servers has become a recent research thrust to meet the increasing demand of network-based services. In this paper, we propose a new Web server architecture, called multi-threaded PIPELINED Web server, suitable for Symmetric Multi-Processor (SMP) or System-on-Chip (SoC) architectures. The proposed PIPELINED model consists of multiple thread pools, where each thread pool consists of five basic threads and two helper threads. The main advantages of the proposed model are global information sharing by the threads, minimal synchronization overhead due to less number of threads, and non-blocking I/O operations, possible with the helper threads.We have conducted an in-depth performance analysis of the proposed server model along with four prior Web server models (Multi-Process (MP), Multi-Thread (MT), Single-Process Event-Driven (SPED) and Asynchronous Multi-Process Event-Driven (AMPED)) via simulation using six Web server workloads. The experiments are conducted to investigate the impact of various factors such as the memory size, disk speed and numbers of clients. The simulation results indicate that the proposed PIPELINED Web server architecture shows the best performance across all system and workload parameters compared to the MP, MT, SPED and AMPED models. Although the MT and AMPED models show competitive performance with less number of processors, the advantage of the PIPELINED model becomes obvious as the number of processors or clients in an SMP/SoC machine increases. The MP model shows the worst performance in most of the cases. The results indicate that the proposed server architecture can be used in future large-scale SMP/SoC machines to boost system performance.

An SSL Back-End Forwarding Scheme in Cluster-Based Web Servers

State-of-the-art cluster-based data centers consisting of three tiers (Web server, application server, and database server) are being used to host complex Web services such as e-commerce applications. The application server handles dynamic and sensitive Web contents that need protection from eavesdropping, tampering, and forgery. Although the secure sockets layer (SSL) is the most popular protocol to provide a secure channel between a client and a cluster-based network server, its high overhead degrades the server performance considerably and, thus, affects the server scalability. Therefore, improving the performance of SSL-enabled network servers is critical for designing scalable and high-performance data centers. In this paper, we examine the impact of SSL offering and SSL-session-aware distribution in cluster-based network servers. We propose a back-end forwarding scheme, called ssl_with_bf, that employs a low-overhead user-level communication mechanism like virtual interface architecture (VIA) to achieve a good load balance among server nodes. We compare three distribution models for network servers, round robin (RR), ssl_with_session, and ssl_with_bf, through simulation. The experimental results with 16-node and 32-node cluster configurations show that, although the session reuse of ssl_with_session is critical to improve the performance of application servers, the proposed back-end forwarding scheme can further enhance the performance due to better load balancing. The ssl_with_bf scheme can minimize the average latency by about 40 percent and improve throughput across a variety of workloads.

A Load Balancing Scheme for Cluster-based Secure Network Servers

Although the secure sockets layer (SSL) is the most popular protocol to provide a secure channel between a client and a cluster-based network server, its high overhead degrades the server performance considerably, and thus, affects the server scalability. Therefore, improving the performance of SSL-enabled network servers is critical for designing scalable and high performance data centers. In this paper, we examine the impact of SSL offering and SSL-session aware distribution in cluster-based network servers. We propose a backend forwarding scheme, called ssl_with_bf that employs a low-overhead user-level communication mechanism like VIA to achieve good load balance among server nodes. We compare three distribution models for network servers: round robin (RR), ssl_with_session and ssl_with_bf through simulation. The experimental results with 16-node and 32-node cluster configurations show that while session reuse of ss_with_session is critical to improve the performance of application servers, the proposed backend forwarding scheme can further enhance the performance due to better load balancing. The ssl_with_bf scheme can minimize average latency by about 40% and improve throughput across a variety of workloads

Impact of Job Allocation Strategies on Communication-Driven Coscheduling in Clusters

In this paper, we investigate the impact of three job allocation strategies on the performance of four coscheduling algorithms (SB, DCS, PB and CC) in a 16-node Linux cluster. The job allocation factors include Multi Programming Level (MPL), job placement, and communication intensity. The experimental results show that the blocking based coscheduling schemes (SB and CC) have better tolerance to different job allocation techniques compared to the spin based schemes (DCS and PB), and the local scheduling. The results strengthen the case for using blocking based coscheduling schemes in a cluster.

Performance Comparison of Coscheduling Algorithms for Non-Dedicated Clusters Through a Generic Framework

In this paper, we address several key issues in designing coscheduling algorithms for clusters. First, we propose a generic framework for deploying coscheduling techniques by providing a reusable and dynamically loadable kernel module. Second, we implement several communication-driven coscheduling algorithms [dynamic coscheduling (DCS), spin block (SB) and periodic boost (PB)] on a 16- node Linux cluster using the above framework. Third, with exhaustive experimentation using mixed workloads, we observe that unlike PB, which provided the best performance on a Solaris platform, the SB scheme outperforms all other techniques on a Linux platform. Finally, we investigate the impact of several job placement strategies, multiprogramming level (MPL), communication intensity and CPU and I/O intensive jobs on the performance of these coscheduling schemes. The experimental results show that the blocking-based coscheduling scheme (SB) has better tolerance to system workload variation compared with the spin-based schemes (DCS and PB), and overall, the blocking-based coscheduling scheme seems a better choice for non-dedicated Linux clusters.

Exploiting NIC Memory for Improving Cluster-Based Webserver Performance

Improving the performance of Web servers has become a critical issue to handle the increasing demand on various network-based services. In this context, we exploit the local memory of programmable network interface cards (NICs) to improve the performance of cluster-based Web servers, which are increasingly used in designing Web server platforms. We use the NIC memory for caching recently accessed data blocks to improve server performance. We have implemented a prototype of the proposed NIC caching mechanism for a distributed Web server, based on PRESS (Carrera et al., 2002), on an 8-node, Myrinet-connected Linux cluster. Measurements with several server workloads show that NIC caching can enhance throughput by up to 27% compared to the original PRESS Web server without NIC caching, by minimizing the DMA and PCI bus overhead

Improving performance of cluster-based secure application servers with user-level communication

In this paper, we have investigated the performance implications of SSL protocol for providing secure service in a cluster-based application server, and have proposed a backend forwarding scheme for improving server performance through better load balance. The proposed SSL/spl I.bar/with/spl I.bar/bf scheme exploits the underlying user-level communication minimizing the intra-cluster communication overhead. All results in this paper indicate that the proposed backend forwarding scheme is a viable mechanism for improving the performance of application servers in cluster-based data centers.

A comprehensive performance and energy consumption analysis of scheduling alternatives in clusters

Abstract In this paper, we conduct an in-depth evaluation of a broad spectrum of scheduling alternatives for clusters. These include the widely used batch scheduling, local scheduling, gang scheduling, most prior communication-driven coscheduling algorithms-Dynamic Coscheduling (DCS), Spin Block (SB), Periodic Boost (PB), and Co-ordinated Coscheduling (CC)-and a newly proposed HYBRID coscheduling algorithm on a 16-node, Myrinet-connected Linux cluster. Performance and energy measurements using several NAS, LLNL and ANL benchmarks on the Linux cluster provide several conclusions. First, although batch scheduling is currently used in most clusters, the blocking-based coscheduling techniques such as SB, CC and HYBRID and the gang scheduling can provide much better performance even in a dedicated cluster platform. Second, in contrast to some of the prior studies, we observe that blocking-based schemes like SB and HYBRID can provide better performance than spin-based techniques like PB on a Linux platform. Third, the proposed HYBRID scheduling provides the best performance-energy behavior and can be implemented on any cluster with little effort. All these results suggest that blocking-based coscheduling techniques are viable candidates to be used in clusters for significant performance-energy benefits.