Optimized dense matrix multiplication on a manycore architecture. Alternatively, because the gpu cores use threading and wide simd units to maximize throughput at the cost of latency, the memory system is designed to maximize bandwidth to satisfy that throughput, with some latency cost. In recent years interest has grown in multiprocessor architectures that can have several hundred processors sharing memory and all working on solving a single problem. Selected regions from the main dram are mirrored into the diestack using a software managed technique. These onchip and o chip caches form a memory hierarchy and are either managed by hardware or software, or a combination of the two. The performance of softwaremanaged multiprocessor caches on. Current trends and the future of software managed onchip. The flashbased memory hierarchy relies on os support to use ssd as a logical extension of dram. This sim ple model captures the important features of. At any time, each page resides either in main memory or on disk. Memory hierarchy memory hierarchy diagram gate vidyalay.
Dynamic data allocation and task scheduling on multiprocessor. A softwaremanaged memory architecture for multiissue. We model programs as hierarchies of bulk operations with explicit parallelism. The following memory hierarchy diagram is a hierarchical pyramid for computer memory. Although this might complicate programming at their current stage, these systems provide more. Achieving good performance on a modern machine with a multilevel memory hierarchy, and in particular on a machine with software managed memories, requires precise tuning of programs to the. One of the primary challenges in embedded system design is designing the memory hierarchy and restructuring the application to take advantage of it. Ibm in its cell processor 61, intel in its singlechip cloud. The semiconductor industry has been speculating for several years about the prospects for a universal memory um technology that would replace both dram and. A large program on a multilevel machine can easily expose.
This paper presents the design and implementation of an optimizing compiler for architectures with software managed memory hierarchies. This new memory subsystem would be added in parallel to a classic memory system, and optimized for readonly data. According to their characteristics, these emerging nvms are adopted into different levels of a conventional memory hierarchy, which include cache, main memory and storage. Memory hierarchy stalls can originate from instruction cache fetch misses, load. In general, the characteristics of such a location are that it. A novel technique to allocate memory on multiple types of main memory technologies from software application layer. The local data is usually placed in a dense register le array which is private to each sm. Such multiprocessors are characterized by a long memory access time, which makes use of. Achieving good performance on a modern machine with a multilevel memory hierarchy, and in particular on a machine with softwaremanaged memories, requires precise tuning of programs to the. A tuning framework for softwaremanaged memory hierarchies.
The performance of softwaremanaged multiprocessor caches. A comparison of programming models for multiprocessors with. Software managed scratchpad memories spm is a scalable alternative to caches, but the benefit comes at the cost of explicit management of data. We evaluate our framework by measuring the performance of benchmarks that are tuned for a range of machines with different memory hierarchy con gurations. In this paper, we develop an energy consumption model for manycore architectures with softwaremanaged memory hierarchy and we propose a general methodology. Most of the computers were inbuilt with extra storage to run more powerfully beyond the main memory capacity. Software managed onchip memories smcs are onchip caches where software can explicitly read and write some or all of the memory references within a block of caches. They integrate a large number of processing cores in a single chip and instead of a hardwaremanaged cache hierarchy, they usually include a softwaremanaged memory hierarchy, visible to the programmer. A cpu cache hierarchy is arranged to reduce latency of a single memory access stream. Such multiprocessors are characterized by a long memory access time, which makes use of cache memories very important. Compilation for explicitly managed memory hierarchies. Registers a cache on variables software managed firstlevel cache a cache on secondlevel. Small, fast storage used to improve average access time to slow memory. A comparison of programming models for multiprocessors.
As the number of cores increases, cachebased memory hierarchy is becoming a major problem in terms of the scalability and energy consumption. Hierarchical memory system a hierarchical memory system or memory. Such onchip memories include, software managed caches shared memory, or hardware caches, or a combination of both 9. One important ongoing research project is the imirror project that utilizes hybrid memory cube diestacked memory integrated into the memory hierarchy. We are also investigating new structures to make the memory hierarchy efficient. A sm is also associated with a softwaremanaged local memory for shared data accesses by threads within a block.
Besides its use in concert with vls, the dma engine can be used as a software managed prefetcher to replicate some of the functionality of the vru. Exploring data migration for future deepmemory manycore systems. This thesisproposes solutions to the problem of memory hierarchy design and data access management. This solution aims to be transparent for the user and. In this paper, we develop an energy consumption model for manycore architectures with software managed memory hierarchy and we propose a general methodology. Vitural memory the address space is ususally broken into fixed number of blocks pages. A memory hierarchy is the standard solution to the dif. We assume a twolevel softwaremanaged instruction memory hierarchy, where the. Cache memories for pdp11 family computers gordon bell. A sm is also associated with a software managed local memory for shared data accesses by threads within a block.
Memory hierarchy design and its characteristics geeksforgeeks. But for softwaremanaged memory hierarchies, we believe it is better to per. In contrast to many other application programs, a database management. So, fundamentally, the closer to the cpu a level in the memory hierarchy is located. Energy management in softwarecontrolled multilevel memory.
The pentium iii processor has two caches, called the primary or level 1 l1 cache and the secondary or level 2 l2 cache. University of delaware department of electrical and computer. It built the memory hierarchy based on a software action defined as the reference position. In contrast to hardware managed caches, softwaremanaged local memories introduce percore, disjoint address spaces that the software is responsible for keeping coherent. The use of the hierarchy is coordinated by user software, system software, or hardware so that the overall characteristics of the memory system approximate the fast access of the fast technology, and the low perbit cost of the low cost technology. At the other extreme, softwaremanaged local stores fig. A virtual local store vls is mapped into the virtual address space of a process and backed by physical main memory, but is stored in a partition of the hardware. Pdf compilation for explicitly managed memory hierarchies. A cache is a smaller, faster memory, located closer to a processor core, which stores copies of the data from frequently used main memory locations. We evaluate our framework by measuring the performance of benchmarks that are tuned for a range of machines with different memory hierarchy configurations. In computer architecture, the memory hierarchy separates computer storage into a hierarchy. Each node of the machine hierarchy has storage memory and may have the ability to perform computation. Exploits spacial and temporal locality in computer architecture, almost everything is a cache. We propose a memory optimization scheme that minimizes the usage of memory space by discovering the chances of memory reuse with the goal of maximizing the application performance.
A large program on a multilevel machine can easily expose tens or hundreds of inter. Hybrid bandwidth hierarchies that incorporate characteristics of both. External memory or secondary memory comprising of magnetic disk, optical disk, magnetic tape i. Another important issue is to optimize the application code and data for such a customized onchip memory hierarchy. Software engineering for embedded systems second edition, 2019. Nikolopoulos 1hana cloud computing, sap the northern ireland science park queens road, belfast, northern ireland bt3 9dt, united kingdom 2the school of electronics, electrical engineering and computer science, queens university belfast. In those cases where the program andor data is too large to fit in affordable memory, a software managed memory hierarchy can be used. This memory hierarchy design is divided into 2 main types. A thread commonly accesses local, shared and global data through a rich memory hierarchy shown in figure 1a. More importantly, architecturallevel modification is required to facilitate the adoption in different levels, which are introduced in detail in this section. Embedded processors rely on the efficient use of instructionlevel parallelism to answer the performance and energy needs of modern applications. Cache memory, memory management, optimization, software engineering, system software mathematics subject classi cation 2010. There is a tradeoff among the three key characteristics of memory namely. These characteristics result in more context switches, which effectively.
In this paper we present a general framework for automatically tuning general applications to machines with softwaremanaged memory hierarchies. Based on the cache simulation, it is possible to determine the hit and miss rate of caches at different levels of the cache hierarchy. Softwaremanaged scratchpad memories spm is a scalable alternative to caches, but the benefit comes at the cost of explicit management of data. Optimized dense matrix multiplication on a manycore. Nikolopoulos 1hana cloud computing, sap the northern ireland science park queens road, belfast, northern. Memory hierarchy is all about maximizing data locality in the network, disk, ram, cache. In those cases where the program andor data is too large to fit in affordable memory, a softwaremanaged memory hierarchy can be used.
However, to support large address spaces, the os will need a place to stash away portions of address spaces that currently arent in great demand. Secondly, different memory subsystems may present heterogeneity and different characteristics. Spm, a softwaremanaged onchip memory, has been used in cmps as a part of the memory hierarchy to improve system performance. Challenges dram technology has hit scaling and power barriers 5, 9. Besides its use in concert with vls, the dma engine can be used as a softwaremanaged prefetcher to replicate some of the functionality of the vru. To do so, we require an additional level in the memory hierarchy.
Cache hierarchy models can be optionally added to a simics system, and the system configured to send data accesses and instruction fetches to the model of the cache system. A tuning framework for softwaremanaged memory hierarchies core. Because it is the softwares responsibility to manage data, the programmer can explicitly manage locality. For example, a gpu may have its own memory subsystem 7 similarly for pim.
Energy management in softwarecontrolled multilevel. A memory optimization technique for software managed. For example, most programs have simple loops which cause instructions and. However, cuda 6 introduces unified memory by which the data in the host memory can. Performance is critically dependent on how well the hierarchy is managed.
A cpu cache 1 is a hardware cache used by the central processing unit cpu of a computer to reduce the average cost time or energy to access data from the main memory. Memory hierarchy layout with its characteristics throughout the computer system architecture, memory hierarchy is an innovation to arrange memory in such a manner that the storage time can reduce. Softwaremanaged onchip memories smcs are onchip caches where software can explicitly read and write some or all of the memory references within a block of caches. Jul 04, 2018 according to their characteristics, these emerging nvms are adopted into different levels of a conventional memory hierarchy, which include cache, main memory and storage. Apr 17, 2005 energy management in softwarecontrolled multilevel a memory hierarchies o. Our sam hierarchy overcomes the coherence overhead and inflexibility of purely hardwaremanaged memory hierarchies in adapting to variable workloads. The single level memory managingoptimizing approaches i. Citeseerx document details isaac councill, lee giles, pradeep teregowda.
Exploring data migration for future deepmemory manycore. Compared to hardwaremanaged cache, spm is managed by the compiler and. This paper presents the design and implementation of an optimizing compiler for architectures with softwaremanaged memory hierarchies. Virtual memory for accelerator research is still at its very. Softwaremanaged energyefficient hybrid dramnvm main. The designing of the memory hierarchy is divided into two types such as primary internal memory and secondary external memory. Internal memory or primary memory comprising of main. The memory hierarchy design in a computer system mainly includes different storage devices. We believe that machines with such explicitly managed memory hierarchies will become increasingly prevalent in the future. Gpu memory hierarchy includes several memories with very different features, such. Thus far, we have assumed that all pages reside in physical memory. Properties of the technologies in the memory hierarchyedit.
How to model the energy consumption of manycore architectures in order to propose techniques for the design of energy efficient applications is a topic of high interest in the community. Memory accesses usually have a great impact on gpu programs. Memory wall computer memory hierarchical storage management cloud storage memory access pattern. Splitting functions in code management on scratchpad memories. In addition, onchip memory hierarchies are also deployed in gpus in order to provide high bandwidth and low latency, particularly for data sharing among spmd threads employing the bsp model as discussed in sect.
This letter proposes a system architecture for a scalable softwareassisted memory sam hierarchy for emerging manycore embedded systems. Analytical models and techniques for softwaremanaged energyef. University of delaware department of electrical and. We can infer the following characteristics of memory.
Although our softwaremanaged onchipinstructionmemoryis similar in performanceenergy characteristics to a conventional hardwaremanaged onchip cache memory, its management is very different from that of. Softwaremanaged energyefficient hybrid dramnvm main memory. Combined with intelligent processorsinmemory pim features to do. This idea is similar to the one in harvard architecture where instruction and data are handled in di erent memories. An example of a user software managed hierarchy is coredisk overlaying. This paper analyzes the current trends for optimizing the use of these smcs. When the cpu references an item within a page that is not in the cache or main memory, a page fault occurs, and the entire page is then moved from the disk to main memory.