43225887
DMMX: Dynamic memory management extensions
Dynamic memory management allows programmers to be more productive and increases system reliability and functionality. However, software algorithms for memory management are slow and non-deterministic. It is well known that object-oriented applications tend to be dynamic memory intensive. This has led programmers to eschew dynamic memory allocation for many real-time and embedded systems. Instead, programmers using Java or C++ as a development language frequently decide to allocate memory statically instead of dynamically. In this paper, we present the design of a bitmap-based memory allocator implemented primarily in combinational logic to allocate memory in a small, predictable amount of time. It works in conjunction with an application-specific instruction-set extension called the dynamic memory management extension (DMMX). Allocation is done through a complete binary tree of combinational logic, which allows constant-time object creation. The garbage collection algorithm is mark sweep, where the sweeping phase can be accomplished in constant time. This hardware scheme can greatly improve the speed and predictability of dynamic memory management. The proposed DMMX is an add-on approach, which allows easy integration into any CPU, hardware-implemented Java virtual machine, or processor in memory.
1021056
A performance perspective on the Active Memory System
Abstract One major problem of using Java in real-time and embedded devices is the non-deterministic turnaround time of dynamic memory management systems (memory allocation and garbage collection). For the allocation, the non-determinism is often contributed by the time to perform searching, splitting, and coalescing. For the garbage collection, the turnaround time is usually determined by the size of the heap, the number of live objects, the number of object collected, and the amount of garbage collected. Even with the current state-of-the-art garbage collectors (generational and incremental schemes), they may or may not guarantee the worst-case latency. Moreover, such schemes often prolong overall garbage collection time. In this paper, the performance analysis of the proposed Active Memory Module (AMM) for embedded systems is presented. Unlike the software counterparts, the AMM can perform a memory allocation in a predictable and bounded fashion (14 cycles). Moreover, it can also yield a bounded sweeping time regardless of the number of live objects or heap size. By utilizing the proposed system, the overall speedup can be as high as 23% compared to the garbage collection system of the JDK 1.2.2 running in classic mode.
39527990
FPGA-based reconfigurable computing
18001825
Architectural support for dynamic memory management
Recent advances in software engineering, such as graphical user interfaces and object-oriented programming, have caused applications to become more memory intensive. These applications tend to allocate dynamic memory prolifically. Moreover, automatic dynamic memory reclamation (garbage collection, GC) has become a popular feature in modern programming languages. As a result, the time consumed by dynamic storage management can be up to one-third of the program execution time. This illustrates the need for a high-performance memory management scheme. This paper presents a top-level design and evaluation of the proposed instruction extensions to facilitate heap management.
12198410
Scalable hardware-algorithm for mark-sweep garbage collection
The memory-intensive nature of object-oriented languages such as C++ and Java has created the need for high-performance dynamic memory management. Object-oriented applications often generate higher memory intensity in the heap region. Thus, a high-performance memory manager is needed to cope with such applications. As today's VLSI technology advances, it becomes increasingly attractive to map software algorithms such as malloc(), free() and garbage collection into hardware. This paper presents a hardware design of a sweeping function (for mark-and-sweep garbage collection) that fully utilizes the advantages of combinational logic. In our scheme, the bit sweep can detect and sweep the garbage in a constant time. Bit-map marking in software can improve the cache performance and reduce number of page faults; however, it often requires several instructions to perform a single mark. In our scheme, only one hardware instruction is required per mark. Moreover, since the complexity of the sweeping phase is often higher than the marking phase, the garbage collection time may be substantially improved. The hardware complexity of the proposed scheme (bit-sweeper) is O(n), where n represents the size of the bit map.
9645285
Using scratchpad to exploit object locality in Java
Performance of modern computers is tied closely to the effective use of cache because of the continually increasing speed discrepancy between processors and main memory. We demonstrate that generational garbage collection employed by a system with cache and scratchpad memory can take advantage of the locality of small short-lived objects in Java and reduce memory traffic by as much as 20% when compared to a cache-only configuration. Converting half of the cache to scratchpad can be more effective at reducing memory traffic than doubling or even quadrupling the size of the cache for several of the applications in SPECjvm98.
29352440
Induced matchings in asteroidal triple-free graphs
An induced matching M of a graph G is a set of pairwise nonadjacent edges such that no two edges of M are joined by an edge in G. The problem of finding a maximum induced matching is known to be NP-hard even for bipartite graphs of maximum degree four. In this paper, we study the maximum induced matching problem on classes of graphs related to AT-free graphs. We first define a wider class of graphs called the line-asteroidal triple-free (LAT-free) graphs which contains AT-free graphs as a subclass. By examining the square of line graph of LAT-free graphs, we give a characterization of them and apply this for showing that the maximum induced matching problem and a generalization, called the maximum δ-separated matching problem, on LAT-free graphs can be solved in polynomial time. In fact, our result can be extended to the classes of graphs with bounded asteroidal index. Next, we propose a linear-time algorithm for finding a maximum induced matching in a bipartite permutation (bipartite AT-free) graph using the greedy approach. Moreover, we show that using the same technique the minimum chain subgraph cover problem on bipartite permutation graphs can be solved with the same time complexity.
9862925
Powers of Asteroidal Triple-free Graphs with Applications
An asteroidal triple is an independent set of three vertices in a graph such that every two of them are joined by a path avoiding the closed neighborhood of the third. Graphs without asteroidal triples are called AT-free graphs. In this paper, we show that every AT-free graph admits a vertex ordering that we call a 2-cocomparability ordering. The new suggested ordering generalizes the cocomparability ordering achievable for cocomparability graphs. According to the property of this ordering, we show that every proper power G (k ≥ 2) of an AT-free graph G is a cocomparability graph. Moreover, we demonstrate that our results can be exploited for algorithmic purposes on AT-free graphs.
17161223
Speculative incoherent cache protocols
Multiprocessing and multithreading are becoming ubiquitous even on single chips. With increasing cache sizes, coherence misses in such systems will account for a larger fraction of all cache misses. As communication latencies increase, this larger fraction of coherence misses will cause significant and increased performance losses. Tuning coherence protocols for specific communication patterns and applications can reduce communication latencies. However, these optimizations increase a protocol's design complexity, making the protocol difficult to verify. A competing approach requires parallel programmers to tune applications to work well with simpler protocols. Speculative execution has successfully improved performance in various scenarios. We propose a new type of load speculation, called coherence decoupling. Coherence decoupling is a microarchitectural mechanism that implements separate protocols for speculative use and for the eventual verification of values. The technique reduces the effect of long communication latencies while mitigating the burdens on the coherence protocol designer and the parallel programmer
7532286
Finding recent frequent itemsets adaptively over online data streams
A data stream is a massive unbounded sequence of data elements continuously generated at a rapid rate. Consequently, the knowledge embedded in a data stream is more likely to be changed as time goes by. Identifying the recent change of a data stream, specially for an online data stream, can provide valuable information for the analysis of the data stream. In addition, monitoring the continuous variation of a data stream enables to find the gradual change of embedded knowledge. However, most of mining algorithms over a data stream do not differentiate the information of recently generated transactions from the obsolete information of old transactions which may be no longer useful or possibly invalid at present. This paper proposes a data mining method for finding recent frequent itemsets adaptively over an online data stream. The effect of old transactions on the mining result of the data steam is diminished by decaying the old occurrences of each itemset as time goes by. Furthermore, several optimization techniques are devised to minimize processing time as well as main memory usage. Finally, the proposed method is analyzed by a series of experiments.
14320982
Sequential Pattern Mining in Multi-Databases via Multiple Alignment
To efficiently find global patterns from a multi-database, information in each local database must first be mined and summarized at the local level. Then only the summarized information is forwarded to the global mining process. However, conventional sequential pattern mining methods based on support cannot summarize the local information and is ineffective for global pattern mining from multiple data sources. In this paper, we present an alternative local mining approach for finding sequential patterns in the local databases of a multi-database. We propose the theme of approximate sequential pattern mining roughly defined as identifying patterns approximately shared by many sequences. Approximate sequential patterns can effectively summerize and represent the local databases by identifying the underlying trends in the data. We present a novel algorithm, ApproxMAP, to mine approximate sequential patterns, called consensus patterns, from large sequence databases in two steps. First, sequences are clustered by similarity. Then, consensus patterns are mined directly from each cluster through multiple alignment. We conduct an extensive and systematic performance study over synthetic and real data. The results demonstrate that ApproxMAP is effective and scalable in mining large sequences databases with long patterns. Hence, ApproxMAP can efficiently summarize a local database and reduce the cost for global mining. Furthremore, we present an elegant and uniform model to identify both high vote sequential patterns and exceptional sequential patterns from the collection of these consensus patterns from each local databases.