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In modern SoCs embedded memories should be protected by ECC against field failures to achieve acceptable reliability. They should also be repaired after fabrication to achieve acceptable fabrication yield. In technologies affected by high defect densities, conventional repair induces very high costs. To reduce it, we can use ECC-based repair, consisting in using the ECC for fixing words comprising a single faulty cell and self-repair to fix all other faulty words. However, as we show in this paper, for high defect densities the diagnosis circuitry required for ECC-based repair may induce very large hardware cost. To fix this issue, we introduce a new family of memory test algorithms that exhibit a property we termed as “single-read double-fault detection”. This approach gains interest in ultimate CMOS and post-CMOS technologies, where the defect densities are expected to increase significantly, and/or in very-low power design, as very-low voltage sharply increases defect densities. [ABSTRACT FROM PUBLISHER]

Branch-and-bound approaches are promising in pruning fruitless search space during the resource constrained scheduling. However, such approaches only compare the estimated upper and lower bounds of an incomplete schedule to the length of the best feasible schedule at that iteration, which does not fully exploit the potential of the pruning during the search. Aiming to improve the performance of resource constrained scheduling, this paper proposes a parallel structure-aware pruning approach that can traverse the search space significantly faster than state-of-the-art branch-and-bound techniques. This paper makes three major contributions: i) it proposes an efficient pruning technique using the structural scheduling information of the obtained best feasible schedules; ii) it investigates how to perform parallel search to enable efficient multi-directional search and generation of effective fences by tuning the operation enumeration order; and iii) it presents a framework that supports the sharing of minimum upper-bound and fence information among different search tasks to enable efficient parallel structure-aware pruning. The experimental results demonstrate that our parallel pruning approach can drastically reduce the overall resource constrained scheduling time under a wide variety of resource constraints. [ABSTRACT FROM PUBLISHER]

Architecting PCM, especially MLC PCM, as main memory for MCUs is a promising technique to replace conventional DRAM deployment. However, PCM/MLC PCM suffers from long write latency and large write energy. Recent work has proposed a compiler directed dual-write (CDDW) scheme to combat the drawbacks of PCM by adopting fast or slow mode for different write operations. For large-scale loops, we observe that write instances' lifetime is very long and can only be written by the expensive slow mode. This paper proposes a write mode aware loop tiling approach to effectively reduce the lifetime of write instances and maximize the number of efficient fast writes in loops. The experimental results show that the proposed approach improves performance by 50.8 percent and reduces dynamic energy by 32.0 percent across a set of benchmarks compared to the CDDW approach on average. [ABSTRACT FROM AUTHOR]

Fairness is an important property of computer networks and systems. In a wide range of these systems such as distributed multi-hop wireless networks, multihomed networks, and cloud computing, each user may be allocated a number of system resources; this resembles a many-to-many relationship between the sets of users and resources, which raises the problem of system-wide fair resource allocation. In this paper, we assume that each user/node can be allocated a number of resources, which could be either in its neighborhood or far from it. As a key difference with previous works and through incorporating the concept of “flow”, we model near/far resources allocated to nodes. To attain fair flow control in such systems, first we model this situation by introducing a new multi-server system called multi-ring, in which a server that represents a resource, can serve only a subset of either neighboring or far nodes in the system. Then, we define a centralized optimization problem to attain weighted proportional fairness among all nodes meaning that the sum of allocated capacities from all servers to each node (while considering its flow) is fair. We evaluate fairness properties of multi-ring networks and provide conditions on system parameters under which a system can have a fair resource allocation. Moreover, we present a distributed method to attain fairness in distributed environments, and its stability/convergence is evaluated by non-linear discrete dynamical systems. We present conditions under which the system is stable, and through numerical analysis, we show how to obtain stable system parameters for large systems. The effectiveness of the presented method is studied through extensive numerical evaluation. Results show the success of our method in attaining fairness for various topologies and system parameters, and confirm our stability analysis. A number of systems with fairness issues are also studied as potential applications of our model. [ABSTRACT FROM AUTHOR]

Phase-change memory (PCM) has emerged as a candidate that overcomes the physical limitations faced by DRAM and NAND flash memory. While PCM has desirable properties in terms of scalability and density, it suffers from limited endurance. Repeated writes cause PCM cells to wear out and get permanently stuck at a specific value. Recovering from stuck-at faults through a proactive error correcting scheme is essential for the widespread adoption of PCM. In this paper, we propose Symbol Shifting as a practical technique to increase the number of faults that an error correcting code can cover in single and multilevel cells memory chips. Since stuck-at cells can still be read, errors are manifested only when a worn-out cell is to be programmed with a symbol value different than the value it is stuck at. After a write operation fails for a given block of data, another write operation is attempted with all original data symbols shifted to another memory level. Shifting the data is likely to bring the number of errors within the nominal capability of the deployed error correcting code. Requiring only one additional auxiliary cell, Symbol Shifting can increase the number of faults that an error correcting code can cover by up to double the nominal capability and extends the lifetime by up to 37 percent. [ABSTRACT FROM AUTHOR]

Given a chip that produced a faulty output response to a test set, a defect diagnosis procedure produces a set of candidate faults that is expected to identify the defects that are present in the chip. The accuracy of the set of candidate faults is higher when the set is smaller or when its overlap with the defects that are present in the chip is larger. To increase the accuracy of a set of candidate faults, this paper describes an approach where several sets of candidate faults are computed based on different subsets of the test set. The subsets are obtained by removing small numbers of tests from the complete test set. The result is sets of candidate faults that are similar but not identical. The number of sets where a fault appears yields a confidence level that the fault actually belongs in a set of candidate faults. New sets of candidate faults are defined based on the confidence levels obtained. The smallest set of candidate faults can be used as the final result of defect diagnosis, or the sets can be used for ranking the candidates. Experimental results for benchmark circuits demonstrate the effectiveness of this approach. [ABSTRACT FROM PUBLISHER]

Multi-channel wireless data broadcast is an appropriate approach to disseminate data to a mass number of mobile clients. In this paper, we present a global optimization for multi-channel wireless data broadcast with Alphabetic Huffman Tree (AH-Tree) Indexing scheme, which can deal with skewed access frequencies well. We present three novel designs to reduce the access latency and tuning time of the broadcast system. Firstly, we design a dynamic programming for AH-Tree construction with low time complexity. Compared with traditional Hu-Tucker algorithm in $O(n^k)$ , our algorithm can build a $k$ -ary AH-Tree index in $O(n^2)$ . Next, we depict a new control table design, which eliminates up to 50 percent redundant entries while keeps the searching efficiency. We also theoretically prove that an optimal alphabetic tree has the minimum average tuning time among all tree-based index structures for skewed data broadcast. Thirdly, we design the new index and data allocation algorithms to further reduce the tuning time and access latency. The simulation results validate the effectiveness of our algorithms. In all, our global optimization mechanism can greatly improve the system performance and time efficiency for wireless data broadcast applications. [ABSTRACT FROM AUTHOR]

In network on chips (NoCs) design, reconfiguration of NoC is a very effective option for minimizing power consumption, and Gaussian networks can provide significant advantage over the mesh networks in terms of network diameter, average hop distance and so on. In this paper, based on the special topology structure and the static connection rules within Gaussian networks, we present the reconfiguration representation for Gaussian networks and the nature of reconfigurable Gaussian networks. Furthermore, reconfigurable rules of Gaussian networks are proposed to design the constraints for automatic reconfiguration of NoC. [ABSTRACT FROM PUBLISHER]

Scratchpad memories in GPU architectures are employed as software-controlled caches to increase the effective GPU memory bandwidth. Through the use of well-known optimization techniques, such as privatization and tiling, they are properly exploited. Typically, they are banked memories which are addressed with a \textmod(2^N) bank indexing scheme. Although their bandwidth is fully exploited for linear memory accesses, their performance is burdened when non-unit strides appear in memory access patterns because they provoke bank conflicts. This paper explores the use of configurable bit-vector and bitwise XOR-based hash functions to evenly distribute memory addresses of the access patterns over the memory banks, reducing the number of bank conflicts. An exhaustive, but lightweight, search is used to configure bit-vector hash functions. Bitwise hash functions are configured with heuristics. Hardware and software implementations are carried out. For the hardware approach, the experimental results show 24 percent performance speed-up for 22 benchmarks on GPGPU-Sim, a Fermi-like simulator. Bank conflicts are reduced by 96 percent with bit-vector hash functions, and 97 percent with bitwise hash functions using our proposed Minimum Imbalance Heuristic. The software approach, using bit-vector hash functions, demonstrates 23 percent speed-up and 96 percent bank conflict reduction on a Fermi GPU, and 33 percent speed-up and 99 percent bank conflict reduction on a Kepler GPU. [ABSTRACT FROM AUTHOR]

Automatically predicting performance of parallel applications has been a long-standing goal in the area of high performance computing. However, accurate performance prediction is challenging, since the execution time of parallel applications is determined by several factors, such as sequential computation time, communication time and their complex interactions. Despite previous efforts, accurately estimating the sequential computation time in each process for large-scale parallel applications remains an open problem. In this paper, we propose a novel approach to acquiring accurate sequential computation time using a parallel debugging technique called deterministic replay. The main advantage of our approach is that we only need a single node of a target platform but the whole target platform does not need to be available. Therefore, with this approach we can simply measure the real sequential computation time on a target node for each process on by one. Moreover, we observe that there is great computation similarity in parallel applications, not only within each process but also among different processes. Based on this observation, we further propose representative replay that can significantly reduce replay overhead, because we only need to replay partial iterations for representative processes instead of all of them. Finally, we implement a complete performance prediction system, called Phantom, which combines the above computation-time acquisition approach and a trace-driven simulator. We validate our approach on both traditional HPC platforms and the latest Amazon EC2 cloud platform. On both types of platforms, prediction error of our approach is less than 7 percent on average up to 2,500 processes. [ABSTRACT FROM AUTHOR]

The non-volatile memory (NVM) which can provide DRAM-like performance and disk-like persistency has the potential to build single-level systems by replacing both DRAM and disk. Keeping data consistency in such systems is non-trivial because memory writes may be reordered by CPU. Although ordered memory writes for achieving data consistency can be implemented using the memory fence and the CPU cache line flush instructions, they introduce a significant overhead (more than 10X slower in performance). In this paper, we focus on an important and common data structure, B $^+$ Tree. Based on our quantitative analysis for consistent tree structures, we propose NV-Tree, a consistent, cache-optimized and workload-adaptive B $^+$ Tree variant with significantly reduced consistency cost (up to 96 percent reduction in CPU cache line flush). To further optimize NV-Tree under various workloads, we propose a workload-adaptive scheme in which the sizes of individual nodes can be dynamically adjusted to improve the performance over time. We implement and evaluate NV-Tree and NV-Store, a key-value store based on NV-Tree, on an NVDIMM server. NV-Tree outperforms the state-of-art consistent tree structures by up to 12X under write-intensive workloads. NV-Store increases the throughput by up to 7.3X under YCSB workloads compared to Redis. [ABSTRACT FROM AUTHOR]

Networks-on-chip (NoCs) have been increasingly adopted in recent years due to the extensive integration of many components in modern multicore processors and system-on-chip designs. At the same time, transistor reliability is becoming a major concern due to the continuous scaling of silicon. As the sole medium of on-chip communication, it is critical for a NoC to be able to tolerate many permanent transistor failures. In this paper, we propose uDIREC, a unified framework for permanent fault diagnosis and subsequent reconfiguration in NoCs, which provides graceful performance degradation with an increasing number of faults. Upon in-field transistor failures, uDIREC leverages a fine-resolution diagnosis mechanism to disable faulty components very sparingly. At its core, uDIREC employs MOUNT, a novel routing algorithm to find reliable and deadlock-free routes that utilize all the still-functional links in the NoC. We implement uDIREC's reconfiguration as a truly-distributed hardware solution, still keeping the area overhead at a minimum. We also propose a software-implemented reconfiguration that provides greater integration with our software-based diagnosis scheme, at the cost of distributed nature of implementation. Regardless of the adopted implementation scheme, uDIREC places no restriction on topology, router architecture and number and location of faults. Experimental results show that uDIREC, implemented in a 64-node NoC, drops 3 $\times$ fewer nodes and provides greater than 25 percent throughput improvement (beyond 15 faults) when compared to other state-of-the-art fault-tolerance solutions. uDIREC's improvement over prior-art grows further with more faults, making it a effective NoC reliability solution for a wide range of fault rates. [ABSTRACT FROM AUTHOR]

As a result of huge advancements in VLSI technology, more and more complex circuits are being implemented making not only the whole digital system more prone to faults, but also the fault detector itself susceptible to faults resulting in the requirement of concurrent fault detection architecture of the encoders and decoders. In this paper, we present a multiple-bit parity-based fault detection architecture for parallel CRC computation. After analyzing the parallel implementation of CRC, we present a formulation to generate a multiple-bit parity prediction structure to incorporate the fault detection architecture. Using the formulations of digit level CRC architecture, the checksum is divided into few blocks and predicted multiple-bit parity of the blocks are compared with the actual parity bits. Finally, with the help of software simulation and ASIC implementation, we show that the proposed scheme is highly efficient in terms of fault detection capability whereas it involves small area and time overhead. As an example, we have shown that the worst case area overhead is $25.7$ percent for CRC $-32$ with four parity bits, and corresponding time overhead is $15.6$ percent. [ABSTRACT FROM PUBLISHER]

Access control is an indispensable security component of cloud computing, and hierarchical access control is of particular interest since in practice one is entitled to different access privileges. This paper presents a hierarchical key assignment scheme based on linear-geometry as the solution of flexible and fine-grained hierarchical access control in cloud computing. In our scheme, the encryption key of each class in the hierarchy is associated with a private vector and a public vector, and the inner product of the private vector of an ancestor class and the public vector of its descendant class can be used to derive the encryption key of that descendant class. The proposed scheme belongs to direct access schemes on hierarchical access control, namely each class at a higher level in the hierarchy can directly derive the encryption key of its descendant class without the need of iterative computation. In addition to this basic hierarchical key derivation, we also give a dynamic key management mechanism to efficiently address potential changes in the hierarchy. Our scheme only needs light computations over finite field and provides strong key indistinguishability under the assumption of pseudorandom functions. Furthermore, the simulation shows that our scheme has an optimized trade-off between computation consumption and storage space. [ABSTRACT FROM PUBLISHER]

In this paper, a new family of formats to deal with real number for applications requiring round to nearest is proposed. They are based on shifting the set of exactly represented numbers which are used in conventional radix- $\beta$ number systems. This technique allows performing radix complement and round to nearest without carry propagation with negligible time and hardware cost. Furthermore, the proposed formats have the same storage cost and precision as standard ones. Since conversion to conventional formats simply require appending one extra-digit to the operands, standard circuits may be used to perform arithmetic operations with operands under the new format. We also extend the features of the RN-representation system and carry out a thorough comparison between both representation systems. We conclude that the proposed representation system is generally more adequate to implement systems for computation with real number under round-to-nearest. [ABSTRACT FROM PUBLISHER]

Software Transactional Memory (STM) has recently emerged as a promising synchronization abstraction for multicore architectures. State-of-the-art STM algorithms, however, suffer from performance challenges due to contention and spinning on locks during the transaction commit phase. In this paper, we introduce Remote Transaction Commit (or RTC), a mechanism for executing commit phases of STM transactions. RTC dedicates server cores to execute transactional commit phases on behalf of application threads. This approach has two major benefits. First, it decreases the overheads of spinning on locks during commit, such as the number of cache misses, blocking of lock holders, and CAS operations. Second, it enables exploiting the benefits of coarse-grained locking algorithms (simple and fast lock acquisition, reduced false conflicts) and bloom filter-based algorithms (concurrent execution of independent transactions). Our experimental study on a 64-core machine with four sockets shows that RTC solves the problem of performance degradation due to spin locking on both micro-benchmarks (red-black trees), and macro-benchmarks (STAMP), especially when the commit phase is relatively long and when thread contention increases. [ABSTRACT FROM PUBLISHER]

We consider a competitive environment for reward-based scheduling of periodic tasks, where the execution of each task consists of a mandatory and an optional part. Each task obtains a value if the processor successfully schedules all its mandatory part, and also an additional reward value if the processor successfully schedules a part of its optional execution. Each task is owned by a self-interested agent who has multiple choices for its requests based on its optional part. We model the reward-based scheduling problem by considering such multi-minded agents. However, the agent may try to manipulate the system to obtain an unfair optional allocation. We address this challenge by designing novel truthful mechanisms in which it is always in the agent's best interest to report their true task characteristics. We propose two truthful mechanisms (an exact and approximate) for selecting a feasible subset of agents and an allocation of optional execution that maximizes the total reward obtained by the selected tasks. To address the pseudo-polynomial complexity of the exact mechanism, we show that our proposed approximate mechanism is a polynomial-time approximation scheme (PTAS). Our extensive experiments show that our proposed approximation mechanism is capable of finding near-optimal solutions efficiently while guaranteeing truthfulness. [ABSTRACT FROM PUBLISHER]

Due to their high density, modern DRAMs are very susceptible to the interactions between adjacent cells, which in turn increases the difficulty and complexity of memory testing. In this work, we studied the interaction mechanisms among neighbouring DRAM cells in order to provide an efficient testing solution. According to the open literature, there are two mechanisms responsible for this interaction: leakage currents and cell state transitions. The frequently used Coupling Fault (CF) model is inadequate to model the combined effect of these mechanisms, while testing procedures using the Neighborhood Pattern Sensitive Fault (NPSF) model are not time efficient solutions. Towards this direction, we propose a new fault model, the Neighborhood Leakage and Transition Fault (NLTF) model for DRAMs, which effectively models the faulty behavior related to neighbouring cell interference. In addition, we developed a new test algorithm which is based on the NLTF model, and provides test application time reductions ranging from 68 to 87 percent with respect to the existing testing algorithms in the literature that are capable to cover the NLTFs. Finally, the proposed algorithm is extended to cover NLTFs in word-oriented DRAMs. [ABSTRACT FROM AUTHOR]

We introduce an algorithm to compare a binary floating-point (FP) number and a decimal FP number, assuming the “binary encoding” of the decimal formats is used, and with a special emphasis on the basic interchange formats specified by the IEEE 754-2008 standard for FP arithmetic. It is a two-step algorithm: a first pass, based on the exponents only, quickly eliminates most cases, then, when the first pass does not suffice, a more accurate second pass is performed. We provide an implementation of several variants of our algorithm, and compare them. [ABSTRACT FROM PUBLISHER]