On the efficiency of vector computers with private cache memories

Software transparent cache consistency scheme for a VMEbus-based system

Two performance gaps in the memory hierarchy, between CPU cache and main memory, and main memory and mass storage, will become increasingly severe bottlenecks for computing-system performance. Although it is necessary to increase memory capacity to fill these gaps, power also increases when conventional volatile memories are used. A new nonvolatile memory for this purpose has been anticipated. Storage class memory is used to fill the second gap. Many candidates exist: ReRAM, PRAM, and 3D-cross point type with resistive change RAM. However, nonvolatile last level cache (LLC) is used to fill the first gap. Advanced STT-MRAM has achieved sub-4ns read and write accesses with perpendicular magnetic tunnel junctions (p-MTJ) [1–2]. Furthermore, mature integration processes have been developed and 8Mb STT-MRAM with sub-5ns operation has shown high reliability [3]. Moreover, because of its non-volatility, STT-MRAM can reduce operation energy by more than 81% compared to SRAM for cache [1]. This paper presents STT-MRAM-based last level cache memory (LLC) including MRAM memory core, peripherals and cache logic circuits, using novel power optimization with high-speed power gating (HS-PG),considering processor architectures and cache memory accesses. The STT-MRAM-based cache has high reliability to reduce the write-error rate with novel write-verify-write. Furthermore, a read-modify-write scheme is implemented to reduce active power without penalty. Figure 7.2.1 presents a block diagram of a 4Mb STT-MRAM based cache.

Cache memory has grown to be an essential component of CPU architecture due to the growing gap between processing power and main memory access latency. The cache design that processors use has numerous levels, with the smallest, fastest private caches (Level 1) supported to the largest, slowest caches (Level 2). Snoop Control Units (SCUs) have been added to multi-core processors to ensure the coherency of private cache data. The literature that is currently available discusses application-specific cache alignment methods. When inter-core communication begins to function at the OS level, Symmetric Multi-Processing (SMP)/Asymmetric Multi-Processing (AMP) Real Time Operating Systems (RTOS) will add a significant amount of overhead to system activities. This study is the first to propose an unique signalling technique between the cores based on cache aware information lookups. It is implemented as "SCHEDULE-ASSIST" and "ENTITY-ASSIST" in the Little Kernel scheduler, an SMP RTOS scheduler. We demonstrate an up to 13% improvement in RTOS processing Key Performance Indices (KPI) for RTOS’ Application Programming Interfaces (APIs) compared to schemes that are unaware of the cache design through analytical modelling and implementation using a Xilinx Evaluation Kit.

Summary form only given. An approach towards an information theoretic based analysis and design of cache memories is presented. Computer systems usually have a slow main memory and a faster cache memory, usually much smaller than the main memory because of its cost. A somewhat similar situation is present also in Internet servers. A miss happens whenever an item is not found in the cache memory. If so, the item is fetched from the main memory and placed in the cache. A hit is obtained whenever the item is found in the cache. Usually the cost of a miss is several times that of a hit. The goal is to find strategies for the many to one mapping of addresses of the main memory to the cache memory, as well as the replacement strategies. Usual replacement strategies are least recently used, LRU, random replacement, RR, etc. The main goal is to obtain strategies that will optimize the running time of the program under execution. Since almost all programs use branch instructions and loops, some of the information theoretic approaches previously introduced consider the prediction of the result of a branch based on its past behavior. Here a different approach is considered. In particular the opposite case is analysed, i.e. a linear loop that is executed indefinitely. In particular a combined random replacement and least recently used strategy is analyzed. It is shown that this model is equivalent to the one of classifying N objects in M classes with at least c objects in each class, and that this problem gives a generalization of the Ehrenfests' urn model used in statistical thermodynamics in connection with the Boltzmann H-theorem.

Large-scale MIN-based shared-memory multiprocessor systems have long shared memory latency. Private caches can improve memory access latency but they may suf fer from the cache coherence problem and potentially lower data locality due to data sharing and multiproces sor scheduling. These two problems also increase shared memory load and may result in frequent memory stalls. In this paper, we evaluate the performance of memory caches, a cache memory placed in front of shared memory, in a large-scale multiprocessor system in the presence of pro cessor caches. The memory cache is shown to have good performance and scalability.

Random Access Memory plays a crucial role in data processing in various computing systems for faster applications. A processor always fetches the data from the main memory for processing, sometimes the same data may be required for the processing and need to be fetched repeatedly from the main memory results time consuming. Cache memory supports faster data storage and access by storing instances of programs and data which is routinely accessed by the processor. Therefore, the cache memory is used to store recently fetched data and when a processor requests to fetch the data the controller will first check the data in cache, if the fetched data is there in the cache then it will be fetched otherwise the controller will fetch the data from the main memory. Therefore, the cache memory is useful for improving speed of processing without wasting much time for fetching the repeated data. This paper deals with various structures of single ended S-RAM cells and proposes a novel three transistor S -RAM cell design Using Tanner 45nm Technology.

Nonvolatile random access memory (NVRAM) is becoming a popular alternative as the memory and storage medium in battery-powered embedded systems because of its fast read/write performance, byte-addressability, and nonvolatility. A well-known example is phase-change memory (PCM) that has much longer life expectancy and faster access performance than NAND flash. When NVRAM is considered as both main memory and storage in battery-powered embedded systems, existing page cache mechanisms have too many unnecessary data movements between main memory and storage. To tackle this issue, we propose the concept of “union page cache,” to jointly manage data of the page cache in both main memory and storage. To realize this concept, we design a partial page cache strategy that considers both main memory and storage as its management space. This strategy can eliminate unnecessary data movements between main memory and storage without sacrificing the data integrity of file systems. A series of experiments was conducted on an embedded platform. The results show that the proposed strategy can improve the file accessing performance up to 85.62% when PCM used as a case study.

Introduces an innovative cache design for vector computers, called prime-mapped cache. By utilizing the special properties of a Mersenne prime, the new design does not increase the critical path length of a processor, nor does it increase the cache access time as compared to existing cache organizations. The prime-mapped cache minimizes cache miss ratio caused by line interferences that have been shown to be critical for numerical applications by previous investigators. With negligibly additional hardware cost, significant performance gains are obtained by adding the proposed cache memory to an existing vector computer. The performance of the design is studied analytically, using a generic vector computation model. The analytical model is validated through extensive simulation experiments. A performance analysis for various vector access patterns shows that the prime-mapped cache performs significantly better than conventional cache organizations in the vector processing environment. The performance gain will increase with the increase of the speed gap between processors and memories. >

In this paper, we propose a software shared virtual memory (SVM) system for heterogeneous multicore accelerator clusters with explicitly managed memory hierarchies. The target cluster consists of a single manager node and many compute nodes. The manager node contains a generalpurpose processor and larger main memory, and each compute node contains a heterogeneous multicore processor and smaller main memory. These nodes are connected with an interconnection network, such as Gigabit Ethernet. The heterogeneous multicore processor in each compute node consists of a general-purpose processor element (GPE) and multiple accelerator processor elements (APEs). The GPE runs an OS and the multiple APEs are dedicated to compute-intensive workloads. The GPE is typically backed by a deep on-chip cache hierarchy and hardware cache coherence. On the other hand, the APEs have small explicitly-addressed local memory instead of caches. This APE local memory is not coherent with the main memory. Different main and local memory units in the accelerator cluster can be viewed as an explicitly managed memory hierarchy: global memory, node local memory, and APE local memory. Since coherence protocols of previous software SVM proposals cannot effectively handle such a memory hierarchy, we propose a new coherence and consistency protocol, called hierarchical centralized release consistency (HCRC). Our software SVM system is built on top of HCRC and software-managed caches. We evaluate the effectiveness and analyze the performance of our software SVM system on a 32-node heterogeneous multicore cluster (a total of 192 APEs).

Modern large-scale computer systems require interconnection networks that are both high-performance and energy efficient. Most large-scale systems are made from a large number of “nodes”, where each node has one or more computing elements and a block of main memory, and is connected to a network that interconnects all of the nodes. There are several factors influencing the evolution of systems that has lead to this configuration: (1) as these components are all based on consumer products, the costs have become very low, as compared to customized components, (2) many problems require very large amounts of main memory (for efficient execution), and the best way to have sufficient memory capacity is to use many smaller discrete blocks of memory, as opposed to one or a few large blocks of memory, and (3) this arrangement of distributed nodes offers opportunities for maximum levels of parallel computation.

Faster joins, self-joins and multi-way joins using join indices

Main memory contains transient information for all resident applications. However, if memory chip contents survives power-off, e.g., via freezing DRAM chips, sensitive data such as passwords and keys can be extracted. Main memory persistence will soon be the norm as recent advancements in MRAM and FeRAM position non-volatile memory technologies for widespread deployment in laptop, desktop, and embedded system main memory. Unfortunately, the same properties that provide energy efficiency, tolerance against power failure, and instant-on'' power-up also subject systems to offline memory scanning. In this paper, we propose a memory encryption control unit (MECU) that provides memory confidentiality during system suspend and across reboots. The MECU encrypts all memory transfers between the processor-local level 2 cache and main memory to ensure plaintext data is never written to the persistent medium. The MECU design is outlined and performance and security trade-offs considered. We evaluate a MECU-enhanced architecture using the SimpleScalar hardware simulation framework on several hardware benchmarks. This analysis shows the majority of memory accesses are delayed by less than 1 ns, with higher access latencies (caused by resume state reconstruction) subsiding within 0.25 seconds of a system resume. In effect, the MECU provides zero-cost steady state memory confidentiality for non-volatile main memory.

Cache memory hierarchies are used to buffer those portions of main memory with the most frequent use by the CPU. As cache memory is very costly, good design techniques must consider small cache sizes maintaining high levels of use (hit ratio) and ease of implementation. The memory replacement policy is important in maintaining a high hit ratio. Most replacement policies used are easily implemented when the main memory has fixed page locations. A new cache algorithm using a variable page configuration is explained in terms of program behaviour.

Global load instruction aggregation based on dimensions of arrays

In the realm of modern computing, cache memory serves as an essential intermediary, mitigating the speed disparity between rapid processors and slower main memory. Central to this study is the development of an innovative cache controller for a 4-way set associative cache, meticulously crafted using VHDL and structured as a Finite State Machine. This controller efficiently oversees a cache of 256 bytes, with each block encompassing 128 bits or 16 bytes, organized into four sets containing four lines each. A key feature of this design is the incorporation of the Tree Pseudo Least Recently Used (PLRU) algorithm for cache replacement, a strategic choice aimed at optimizing cache performance. The effectiveness of this controller was rigorously evaluated using ModelSim, which generated a comprehensive timing diagram to validate the design's functionality, especially when integrated with a segmented main memory of four 1KB banks. The results from this evaluation were promising, showcasing precise logic outputs within the timing diagram. Operational efficiency was evidenced by the controller's swift processing speeds: read hits were completed in a mere three cycles, read misses in five and a half cycles, and both write hits and misses in three and a half cycles. These findings highlight the controller's capability to enhance cache memory efficiency, striking a balance between the complexities of set-associative mapping and the need for optimized performance in contemporary computing systems. This study not only demonstrates the potential of the proposed cache controller design in bridging the processor-memory speed gap but also contributes significantly to the field of cache memory management by offering a viable solution to the challenges posed by traditional cache configurations.