Publications

In recent years integrating multiprocessors in a single chip is emerging for supporting various scientific and commercial applications, with diverse demands to the underlying on-chip networks. Communication traffic of these applications makes routers greedy to acquire more power such that the total consumed power of the network may exceed the supplied power and cause reliability problems. To ensure high performance and power constraint satisfaction, the on-chip network must have a peak power control mechanism. In this paper, we propose a credit-based peak power control scheme to assure power consumption to be under the given peak power constraint, without performance degradation. The peak power control scheme efficiently regulates each flow’s injection rate at the sender to minimize performance penalty. We have two different throttling schemes for real-time traffic and best-effort traffic; a rate-based throttling and an energy-budget based throttling, respectively. The simulation results on mesh networks show that the credit-based peak power control effectively prevents performance degradation and meets the peak power constraint.

With the growing popularity of cluster architectures in datacenters and the sophistication of computer attacks, the design of highly secure clusters has recently emerged as a critical design issue. However, the majority of cluster security research has focused on how to detect and prevent attacks rather than on how to minimize the effect of attacks once detected. The action against detected attacks in the cluster is as important as the actual detection process since no detection mechanism is full-proof in its ability to protect cluster systems without the effective cluster-wide reaction. In this paper, we propose a scheme, referred to as the Instant Attack Stopper (IAS) that can instantly confront security attacks in a cluster. Specifically we provide detailed implementation methods of IAS in InfiniBand Architecture (IBA) – a new promising communication standard for future System Area Networks (SANs) and clusters. IAS focuses on removing malicious communication on the IBA fabric among processes involved in an attack, which is accomplished through the proposed Security Management Agent (SeMA). We will show IAS deployment in different security levels to meet various security requirements.

Energy efficient design for disk devices has become a very important issue, because ever increasing need for data storage systems significantly increases the power budget in the disk array. Most research on power management in disk devices focuses on the traditional way of stopping disk rotation. In this paper, we propose a new approach in which the energy consumption can be reduced without stopping the disk rotation. The proposed Multiple Idle States (MIS) model modulates the disk RPM to optimize the energy consumption during idle periods. We present a new threshold time model to calculate a minimum idle period so as to save energy without significant performance degradation. The simulation results with real traces show that our MIS achieves more than 58% energy savings at low I/O workload and also gets 8% energy savings for high workload with less than 50% response time compared to the traditional shut-down power management scheme.

With the growing use of cluster systems in web servers, file distribution and database transactions, power conservation and efficiency have been identified as critical issues in the design of cluster systems. Widely adopted, distributor-based systems forward client requests to a balanced set of backend servers in complete transparency to the clients. In this paper, we use power and locality-based request distribution at the distributor to provide optimum power conservation, while maintaining the required QoS of the system. The distribution scheme uses a simple memory management technique using pinned memory on the backend servers and proactive distribution, with the aid of data organization of the website, to improve the locality of the files. A simple on-off based power management scheme is applied to conserve power. Our scheme provides reduced response time to the clients and improved power conservation at the backend server cluster without compromising performance. Simulations involving real-time web traces and latest web technologies witness performance boost of 15- 23% and power conservation of 15-48% over the existing policies.

Designing secure clusters has recently become a critical issue to make these systems robust to attacks from the Internet. The Distributed Denial of Service (DDoS) attack is one of the most serious problems in the current Internet. To defend against DDoS attacks, clusters usually depend on firewalls or Intrusion Detection Systems (IDS). However, once firewall and IDS are breached, the impact of DDoS attack within a cluster can be severe. That is because one infected system or one malicious user, which is believed to be trustworthy, may instantly paralyze the whole cluster through the high speed network. In this paper, we present a deterministic distance packet marking (DDPM) scheme to identify the source nodes generating spoofed IP packets in cluster interconnects. The scheme can be applied to many cluster interconnects such as mesh, torus and hypercube, which are popular in many commercial systems. Our scheme is practically attractive since it is scalable to large networks and does not incur much processing overhead on both switches and nodes.

InfiniBandTM Architecture (IBA) is envisioned to be the default communication fabric for future system area networks (SANs). However, the released IBA specification outlines only higher level functionalities, leaving it open for exploring various design alternatives. In this paper, we investigate four co-related techniques to provide high and predictable performance in IBA. These are: (i) using the Shortest Path First (SPF) algorithm for deterministic packet routing; (ii) developing a multipath routing mechanism for minimizing congestion; (iii) developing a selective packet dropping scheme to handle deadlock and congestion; and (iv) providing multicasting support for customized applications. These designs are evaluated using an integrated workload on a versatile IBA simulation testbed. Simulation results indicate that the SPF routing, multipath routing, packet dropping, and multicasting schemes are quite effective in delivering high and assured performance in clusters. One of the major contributions of this research is the IBA simulation testbed, which is an essential tool to evaluate various design tradeoffs.

Designing energy-efficient clusters has recently become an important concern to make these systems economically attractive for many applications. Since the links and switch buffers consume the major portion of the power budget of the cluster, the focus of this paper is to optimize the energy consumption in these two components. To minimize power in the links, we propose a novel dynamic link shutdown (DLS) technique. The DLS technique makes use of an appropriate adaptive routing algorithm to shutdown the links intelligently. We also present an optimized buffer design for reducing leakage energy. Our analysis on different networks using a complete system simulator reveals that the proposed DLS technique can provide optimized performance-energy behavior (up to 40% energy savings with less than 5% performance degradation in the best case) for the cluster interconnects.

The growing use of clusters in diverse applications, many of which have real-time constraints, requires Quality-of-Service (QoS) support from the underlying cluster interconnect. In this paper, we present an analytical model for a wormhole-switched router with QoS provisioning. In particular, the model captures message blocking due to wormhole switching and bandwidth sharing due to a rate-based scheduling mechanism. Average message latency for dierent trac classes is computed using the model. We evaluate a 16-port router and hypercubes of dierent dimensions with a mixed workload of real-time and best-eort trac. Comparison with the simulation results shows that the single router and the network models are quite accurate in providing the performance estimates.

The growing use of clusters in diverse applications, many of which have real-time constraints, requires Qualityof-Service (QoS) supporr from the underlying cluster interconnect. In this paper; propose an analytical model that captures the characteristics of a QoS capable wormhole router; which is the basic building block of cluster networks. The model captures the behavior of integrated trafic in a cluster and computes tht: average deadline missing probability for real-time trafic. The cluster interconnect, considered here, is a hypercube network. Comparison of Deadline Missing Probability (DkfP) using the proposed model with that of the simulation shows that our analytical model is accurate and useful.