Hsin-Wen Wei

Rate Monotonic Schedulability Conditions Using Relative Period Ratios

Feasibility and schedulability problems have received considerable attention from the real-time systems research community in recent decades. Since the publication of the Liu and Layland bound, many researchers have tried to improve the schedulability bound of the RM scheduling. The LL bound does not make any assumption on the relationship between any of the task periods. In this paper we consider the relative period ratios in a system. By reducing the difference between the smallest and the largest virtual period values in a system, we can show that the RM schedulability bound can be improved significantly. This research has also proposed a system design methodology to improve the schedulability of real-time system with a fixed system load

LaSA: A locality-aware scheduling algorithm for Hadoop-MapReduce resource assignment

Cloud computing has become more popular for a decade; it has been under continuous development with advances in architecture, software, and network. Hadoop-MapReduce is a common software framework processing parallelizable problem across big datasets using a distributed cluster of processors or stand-alone computers. Cloud Hadoop-MapReduce can scale incrementally in the number of processing nodes. Hence, the Hadoop-MapReduce is designed to provide a processing platform with powerful computation. Network traffic is always a most important bottleneck in data-intensive computing and network latency decreases significant performance in data parallel systems. Network bottleneck is caused by network bandwidth and the network speed is much slower than disk data access. So that, good data locality can reduces network traffic and increases performance in data-intensive HPC systems. However, Hadoops scheduler has a defect of data locality in resource assignment. In this paper, we present a locality-aware scheduling algorithm (LaSA) for Hadoop-MapReduce scheduler. Firstly, we propose a mathematical model of weight of data interference in Hadoop scheduler. Secondly, we present the LaSA algorithm to use weight of data interference to provide data locality-aware resource assignment in Hadoop scheduler. Finally, we build an experimental environment with 3 cluster and 35 VMs to verify the LaSAs performance.

CacheRAID: An Efficient Adaptive Write Cache Policy to Conserve RAID Disk Array Energy

Cloud storage is a hot topic at the moment with Googles Google Storage, Microsofts Sky Drive, iCloud, Drop box, Mozy and dozens of others. Because of these applications, conserving energy of storage systems is becoming a growing concern in current storage technology. The factors of disk power consumption include disk idle time, poor random writing performance and random read in distributed file systems. Hence, we present an adaptive write cache mechanism - Cache RAID. Redundant Arrays of Inexpensive Disk (RAID) is widely used in modern distributed storage systems. Our Cache RAID aims to improve the random access problems that implicitly exist in RAID techniques to create more idle time of hard drives, and conserve RAID disk array energy. The experimental results show that Cache RAID storage system can conserved 50%~70% of the power consumption compared to the conventional software RAID system.

New Schedulability Conditions for Real-Time Multiframe Tasks

The real-time multiframe task model first studied by Mok and Chen assumes that the computation times of a periodic task vary instance by instance. They have derived an utilization bound for verifying the schedulability of multiframe task sets. Their schedulability test has since been improved by other researchers. In this paper we use the information about the relative period ratios between tasks in a system to derive a new schedulability condition. By considering the smallest and the largest period values in a system, we can show that the RM schedulability bound can be improved significantly. This method also can be applied to other test methods studied earlier to improve the schedulability of real-time multiframe systems.

Rate monotonic schedulability tests using period-dependent conditions

Abstract Feasibility and schedulability problems have received considerable attention from the real-time systems research community in recent decades. Since the publication of the Liu and Layland bound, many researchers have tried to improve the schedulability bound of the RM scheduling. The LL bound does not make any assumption on the relationship between any of the task periods. In this paper we consider the relative period ratios in a system. By reducing the difference between the smallest and the second largest virtual period values in a system, we can show that the RM schedulability bound can be improved significantly. This research has also proposed a system design methodology to improve the schedulability of real time system with a fixed system load.

Warranty-aware page management for PCM-based embedded systems

The thriving growth in mobile consumer electronics makes energy efficiency in the embedded system design an important and recurring theme. Phase Change Memory (PCM) has shown its potential in replacing DRAM as the main memory option due to its (65%) reduced energy requirements. However, when considering the usage of PCM main memory, its write endurance becomes a critical issue, and wear leveling design is a common approach to resolve this issue. Even though the wear leveling design should stress operation efficiency and overhead reduction, existing wear leveling strategies designed for PCM main memory are usually dedicated to prolonging the lifetime of PCM. In this paper, we propose the perspective that, instead of valuing PCM lifetime exploitation as the first priority, we should turn to satisfy the product warranty period. To this end, further enhancement of operation efficiency and reduction of management overhead could be achieved. We thus propose a warranty-aware page management design to enhance the operation efficiency for managing the endurance issue in PCM. To show the effectiveness of the proposed design, we collected real traces on fiasco. OC by running SPEC2006 benchmarks with different write intensity workloads. The experiment results showed that our design reduced the overhead to one third of that of the state-of-the-art designs while still providing the same level of performance.

Period-Dependent Initial Values for Exact Schedulability Test of Rate Monotonic Systems

Real-time systems using rate monotonic fixed priority scheduling can be checked for schedulability either by pessimistic schedulability conditions or exact testing. Exact testing provides a more precise result but cannot always be performed in polynomial time. Audsley et al. proposed one of the earliest methods by iteratively deriving the job response times. Other researchers have improved the efficiency of their exact test method by using different initial values. All currently proposed initial values do not use the relationship between task periods. In this paper we define initial values using the largest and the second largest periods in a system. We show that the new initial values can significantly improve the exact test.

Enabling Write-Reduction Strategy for Journaling File Systems over Byte-addressable NVRAM

Non-volatile random-access memory (NVRAM) becomes a mainstream storage device in embedded systems due to its favorable features, such as small size, low power consumption, and short read/write latency. On NVRAM, a write operation consumes more energy and time than a read operation. However, current mobile/embedded file systems (e.g., EXT2/3 and EXT4) are very unfriendly for NVRAM devices. The reason is that a journaling mechanism writes the same data twice during data commitment and checkpoint. Such observations motivate this paper to design a two-phase write reduction journaling file system called wrJFS. In the first phase, wrJFS classified data into two categories: Metadata and user data. Metadata will be handled by partial byte-enabled journaling strategy, and user data will be processed in the second phase. In the second phase, user data will be compressed by hardware encoder so as to reduce the write size, and managed compressed-enabled journaling strategy to avoid the write amplification. The experimental results show that the proposed wrJFS can reduce the size of the write request by 89.7% on average, compared with the original EXT3.

Smallest Bipartite Bridge-Connectivity Augmentation

Abstract This paper addresses two augmentation problems related to bipartite graphs. The first, a fundamental graph-theoretical problem, is how to add a set of edges with the smallest possible cardinality so that the resulting graph is 2-edge-connected, i.e., bridge-connected, and still bipartite. The second problem, which arises naturally from research on the security of statistical data, is how to add edges so that the resulting graph is simple and does not contain any bridges. In both cases, after adding edges, the graph can be either a simple graph or, if necessary, a multi-graph. Our approach then determines whether or not such an augmentation is possible. We propose a number of simple linear-time algorithms to solve both problems. Given the well-known bridge-block data structure for an input graph, the algorithms run in O(log n) parallel time on an EREW PRAM using a linear number of processors, where n is the number of vertices in the input graph. We note that there is already a polynomial time algorithm that solves the first augmentation problem related to graphs with a given general partition constraint in O(n(m+nlog n)log n) time, where m is the number of distinct edges in the input graph. We are unaware of any results for the second problem.

An effective monitoring framework and user interface design

A distributed environment requires a monitoring system to oversee the operation of various distributed nodes. A monitoring service is crucial because it ensures a high‐quality computing environment and a reliable service. The interface and framework determine the effectiveness of a monitoring system. This paper uses the concept of user‐adaptive visualization to design its interface and proposes a flexible modular framework. Designers can use the proposed modular framework to flexibly extend existing modules, design visual interfaces to satisfy user requirements, and improve system failover schemes. The implementation of such a monitoring system for monitoring data preservation nodes is also provided. The system including fault‐tolerance and notification functions supports full monitoring services for Storage Resource Broker (SRB) or integrated Rule‐Oriented Data System (iRODS) based systems. The experimental results show that the proposed framework is suitable for data preservation services and is robust and responsive when faced with system failures. Copyright