So the memory organization of the system can be done by memory hierarchy. First, we introduce ldcs using the lu factorization as example in section ii, followed by some preliminary experimental results in a software managed memory hierarchy in section iii. 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 machines particular characteristics. 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. Sequoia code does not make explicit reference to particular.
The first scheme is pure performanceoriented and tuned for extracting the maximum performance possible from the softwaremanaged multilevel memory hierarchy. Softwaremanaged onchip memories shahid alam department of computer science and engineering. First, we introduce ldcs using the lu factorization as example in section ii, followed by some preliminary experimental results in a softwaremanaged memory hierarchy in section iii. Principle at any given time, data is copied between only two adjacent levels. Energy management in softwarecontrolled multilevel. Exploring data migration for future deepmemory manycore systems. Each hardware thread unit has a highspeed onchip sram of 32kb that can be used as a cache. A control statement at level lcan only access data objects scalar variables or array blocks that are placed in the same level l.
A free powerpoint ppt presentation displayed as a flash slide show on id. Architecture we assume a twolevel softwaremanaged instruction memory hierarchy, where the. Hatfield, jeanette gerald program restructuring for virtual memory. Cps104 computer organization and programming lecture 16. A large program on a multilevel machine can easily expose tens. A copy operation is inserted by the framework if a data object resides in one level and it or part of it is needed in another level. One or more memory levels, where a memory level corresponds to a level of hierarchy in a machine a tree of memory modules, with modules at the same depth in the tree having the same memory level. For matrices larger than the data caches, we observed a 46% performance.
Architecting and programming a hardwareincoherent multiprocessor cache hierarchy. A logbased hardware transactional memory with fast. One or more memory levels, where a memory level corresponds to a level of hierarchy in a machine. Every bit that moves through the levels of a supercomputers memory hierarchy has an associated energy cost. Several previous studies have demonstrated the use and bene. Ibm systems journal 103 168192 1971 10 memory hierarchy terminology. Daniel aarno, jakob engblom, in fullsystem simulation with simics, 2015. In fastm, we also change the cache coherence protocol and the l1 cache controller, to guarantee that if there are no over. If an element of an argument is reused inside the task, the reuse is exploited at level l. Ece 550d fundamentals of computer systems and engineering. Citeseerx document details isaac councill, lee giles, pradeep teregowda. We use the terms software controlled memory hierarchy. Exploits memory hierarchy to keep average access time low. 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.
The pentium iii processor has two caches, called the primary or level 1 l1 cache and the secondary or level 2 l2 cache. A compiletime managed multilevel register file hierarchy. Establishing an abstract notion of hierarchical memory is central to the sequoia programming model. Hence, memory access is the bottleneck to computing fast. Citeseerx energy management in softwarecontrolled multi. A tree of memory modules, with modules at the same depth in the tree having the same memory level. Moreover, although one can argue that large exascale.
Memory hierarchy affects performance in computer architectural design, algorithm predictions, and lower level programming constructs involving locality of reference. University of delaware department of electrical and. We believe that machines with such explicitly managed memory hierarchies will become increasingly prevalent in the future. 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 managed cache when active. In this paper we present a general framework for automatically tuning general applications to machines with softwaremanaged memory hierarchies. Optimizing applications for such architectures requires careful management of the data movement across all these levels. If so, we could repeat this process by paging the toplevel page table thus introducing another layer of page table. This thesisproposes solutions to the problem of memory hierarchy design and data access management. Exploits spacial and temporal locality in computer architecture, almost everything is a cache.
In addition, to fully exploit the advantages of emerging nvms, new architectures, such as persistent memory and scm, should be introduced to traditional memory hierarchy. In other words, the physical location of the data stored at a particular address cannot be determined since the onchip caches are automatically managed by the hardware. 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 hardwaremanaged cache when active. Since our baseline system is heavily pipelined to tolerate multicycle register le accesses, accessing operands from di erent levels of the register le hierarchy does not impact performance. 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. The compiler could potentially analyze program behavior and generate instructions to move data up and down the memory hierarchy, shen says. Our mmm implementation overlaps computation with dma block transfers.
Pdf a tuning framework for softwaremanaged memory hierarchies. Apr 17, 2005 energy management in softwarecontrolled multilevel a memory hierarchies o. In other words, the physical location of the data stored at a particular address cannot be determined since the onchip caches are. Practical loop transformations for tensor contraction. We evaluate our framework by measuring the performance of benchmarks that are tuned for a range of machines with different memory hierarchy configurations. It is a part of the chips memorymanagement unit mmu. Current trends and the future of software managed onchip.
Another important issue is to optimize the application code and data for such a customized onchip memory hierarchy. Exploring data migration for future deepmemory manycore. Pdf compilation for explicitly managed memory hierarchies. A translation lookaside buffer tlb is a memory cache that is used to reduce the time taken to access a user memory location. In the design of the computer system, a processor, as well as a large amount of memory devices, has been used. 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. All the stuff in a higher level is in some level below it cs 5 levels in a typical memory hierarchy cs 5 memory hierarchies key principles.
Hardware and software tradeo s for task synchronization on. The problem is then to decide what data to bring to the fast memory at what time and how to decide when data in the fast memory are not useful anymore. A tuning framework for softwaremanaged memory hierarchies. It has several levels of memory with different performance rates. Cache memory design 2 levels in a typical memory hierarchy 3 memory hierarchies key principles locality most programs do not access code or data uniformly smaller hardware is faster goal design a memory hierarchy with cost almost as low as the cheapest level of the hierarchy and speed almost as fast as the fastest level. Abstract memory hierarchy hierarchy of memory components upper levels. Designing for high performance requires considering the restrictions of. A tlb may reside between the cpu and the cpu cache, between. Since response time, complexity, and capacity are related, the levels may also be distinguished by their performance and controlling technologies. At the other extreme, software managed local stores fig. In computer architecture, the memory hierarchy separates computer storage into a hierarchy based on response time. C64 utilizes a dedicated signal bus sigb that allows thread synchronization without any memory bus interference. The tlb stores the recent translations of virtual memory to physical memory and can be called an addresstranslation cache. Performance and energy consumption behavior of embedded applications are increasingly being dependent on their memory usageaccess patterns.
These onchip and o chip caches form a memory hierarchy and are either managed by hardware or software, or a combination of the two. Focusing on a softwaremanaged, applicationspecific multilevel memory hierarchy, this paper studies three different memory hierarchy management schemes. However, the main problem is, these parts are expensive. For many years, cpus have sped up an average of 50% per year over memory chip speed ups. To look up an address in a hierarchical paging scheme, we use the first 10 bits to index into the top level page table. This paper presents the design and implementation of an opti. Such onchip memories include, software managed caches shared memory, or hardware caches, or a combination of both 9. Based on the cache simulation, it is possible to determine the hit and miss rate of caches at different levels of the cache hierarchy. Locality most programs do not access code or data uniformly.
Compilerdirected scratch pad memory hierarchy design and. The hardwaremanaged caches that prevail in the highend computer processors automatically move data through the memory hierarchy in response to the memory requests made by the running application. In this paper we present a general framework for automatically tuning general applications to machines with software managed memory hierarchies. Achieving good performance on a modern machine with a multilevel memory hierarchy, and in particular on a machine with softwaremanaged memories. 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. Registers a cache on variables software managed firstlevel cache a cache on secondlevel. 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. Modern architectures are characterized by deeper levels of memory hierarchy, often explicitly addressable. Scratchpad memory an overview sciencedirect topics.
The first scheme is pure performanceoriented and tuned for extracting the maximum performance possible from the software managed multilevel memory hierarchy. Based on the cache simulation, it is possible to determine the hit and miss rate of caches at different levels. Our model accounts for how the computation is blocked for locality and parallelism and how the hardware handles memory accesses in the caches and the softwaremanaged shared memories. On a cpu, the contents of any memory address may be stored in multiple levels of the memory hierarchy at any given time. This paper analyzes the impact that ldcs can have on the execution time and the power consumption of an application, and presents experimental results performed on two systems. Instead, each level of the hierarchy requires increasing amounts of energy to access. For example, missing the channellevel consideration can result in channellevel imbalance.
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. The second scheme is built upon the first one but it also reduces leakage by turningon and off memory modules i. Energy management in softwarecontrolled multilevel memory. In general, memory modules in a memory level closer to 0 are both smaller and faster than memory modules in a memory level further from 0. Thus, memory architecture modification is required to leverage the advantages of these nvms and mitigate their drawbacks at the same time. This paper analyzes the current trends for optimizing the use of these smcs. Small, fast storage used to improve average access time to slow memory.
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