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259
Algorithms for Scalable Synchronization on Shared-Memory Multiprocessors
- ACM Transactions on Computer Systems
, 1991
"... Busy-wait techniques are heavily used for mutual exclusion and barrier synchronization in shared-memory parallel programs. Unfortunately, typical implementations of busy-waiting tend to produce large amounts of memory and interconnect contention, introducing performance bottlenecks that become marke ..."
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Cited by 567 (32 self)
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Busy-wait techniques are heavily used for mutual exclusion and barrier synchronization in shared-memory parallel programs. Unfortunately, typical implementations of busy-waiting tend to produce large amounts of memory and interconnect contention, introducing performance bottlenecks that become markedly more pronounced as applications scale. We argue that this problem is not fundamental, and that one can in fact construct busy-wait synchronization algorithms that induce no memory or interconnect contention. The key to these algorithms is for every processor to spin on separate locally-accessible ag variables, and for some other processor to terminate the spin with a single remote write operation at an appropriate time. Flag variables may be locally-accessible as a result of coherent caching, or by virtue of allocation in the local portion of physically distributed shared memory. We present a new scalable algorithm for spin locks that generates O(1) remote references per lock acquisition, independent of the number of processors attempting to acquire the lock. Our algorithm provides reasonable latency in the absence of contention, requires only a constant amount of space per lock, and requires no hardware support other than
TreadMarks: Distributed Shared Memory on Standard Workstations and Operating Systems
- IN PROCEEDINGS OF THE 1994 WINTER USENIX CONFERENCE
, 1994
"... TreadMarks is a distributed shared memory (DSM) system for standard Unix systems such as SunOS and Ultrix. This paper presents a performance evaluation of TreadMarks running on Ultrix using DECstation-5000/240's that are connected by a 100-Mbps switch-based ATM LAN and a 10-Mbps Ethernet. Ou ..."
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Cited by 527 (17 self)
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TreadMarks is a distributed shared memory (DSM) system for standard Unix systems such as SunOS and Ultrix. This paper presents a performance evaluation of TreadMarks running on Ultrix using DECstation-5000/240's that are connected by a 100-Mbps switch-based ATM LAN and a 10-Mbps Ethernet. Our objective is to determine the efficiency of a user-level DSM implementation on commercially available workstations and operating systems. We achieved good speedups on the 8-processor ATM network for Jacobi (7.4), TSP (7.2), Quicksort (6.3), and ILINK (5.7). For a slightly modified version of Water from the SPLASH benchmark suite, we achieved only moderate speedups (4.0) due to the high communication and synchronization rate. Speedups decline on the 10-Mbps Ethernet (5.5 for Jacobi, 6.5 for TSP, 4.2 for Quicksort, 5.1 for ILINK, and 2.1 for Water), reflecting the bandwidth limitations of the Ethernet. These results support the contention that, with suitable networking technology, DSM is a...
Evaluation of Release Consistent Software Distributed Shared Memory on Emerging Network Technology
"... We evaluate the effect of processor speed, network characteristics, and software overhead on the performance of release-consistent software distributed shared memory. We examine five different protocols for implementing release consistency: eager update, eager invalidate, lazy update, lazy invalidat ..."
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Cited by 468 (43 self)
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We evaluate the effect of processor speed, network characteristics, and software overhead on the performance of release-consistent software distributed shared memory. We examine five different protocols for implementing release consistency: eager update, eager invalidate, lazy update, lazy invalidate, and a new protocol called lazy hybrid. This lazy hybrid protocol combines the benefits of both lazy update and lazy invalidate. Our simulations indicate that with the processors and networks that are becoming available, coarse-grained applications such as Jacobi and TSP perform well, more or less independent of the protocol used. Medium-grained applications, such as Water, can achieve good performance, but the choice of protocol is critical. For sixteen processors, the best protocol, lazy hybrid, performed more than three times better than the worst, the eager update. Fine-grained applications such as Cholesky achieve little speedup regardless of the protocol used because of the frequency of synchronization operations and the high latency involved. While the use of relaxed memory models, lazy implementations, and multiple-writer protocols has reduced the impact of false sharing, synchronization latency remains a serious problem for software distributed shared memory systems. These results suggest that future work on software DSMs should concentrate on reducing the amount ofsynchronization or its effect.
Shared memory consistency models: A tutorial
- IEEE Computer
, 1996
"... Parallel systems that support the shared memory abstraction are becoming widely accepted in many areas of computing. Writing correct and efficient programs for such systems requires a formal specification of memory semantics, called a memory consistency model. The most intuitive model—sequential con ..."
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Cited by 435 (11 self)
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Parallel systems that support the shared memory abstraction are becoming widely accepted in many areas of computing. Writing correct and efficient programs for such systems requires a formal specification of memory semantics, called a memory consistency model. The most intuitive model—sequential consistency—greatly restricts the use of many performance optimizations commonly used by uniprocessor hardware and compiler designers, thereby reducing the benefit of using a multiprocessor. To alleviate this problem, many current multiprocessors support more relaxed consistency models. Unfortunately, the models supported by various systems differ from each other in subtle yet important ways. Furthermore, precisely defining the semantics of each model often leads to complex specifications that are difficult to understand for typical users and builders of computer systems. The purpose of this tutorial paper is to describe issues related to memory consistency models in a way that would be understandable to most computer professionals. We focus on consistency models proposed for hardware-based shared-memory systems. Many of these models are originally specified with an emphasis on the system optimizations they allow. We retain the system-centric emphasis, but use uniform and simple terminology to describe the different models. We also briefly discuss an alternate programmer-centric view that describes the models in terms of program behavior rather than specific system optimizations. 1
Tolerating Latency Through Software-Controlled Prefetching in Shared-Memory Multiprocessors
- Journal of Parallel and Distributed Computing
, 1991
"... The large latency of memory accesses is a major obstacle in obtaining high processor utilization in large scale shared-memory multiprocessors. Although the provision of coherent caches in many recent machines has alleviated the problem somewhat, cache misses still occur frequently enough that they s ..."
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Cited by 301 (18 self)
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The large latency of memory accesses is a major obstacle in obtaining high processor utilization in large scale shared-memory multiprocessors. Although the provision of coherent caches in many recent machines has alleviated the problem somewhat, cache misses still occur frequently enough that they significantly lower performance. In this paper we evaluate the effectiveness of non-binding software-controlled lyrefetching, as proposed in the Stanford DASH Multiprocessor, to address this problem. The prefetches are non-binding in the sense that the prefetched data is brought to a cache close to the processor, but is still available to the cache coherence protocol to keep it consistent. Prefetching is software-controlled since the program must explicitly issue prefetch instructions.
Transactional memory coherence and consistency
- In ISCA
, 2004
"... In this paper, we propose a new shared memory model: Transactional ..."
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Cited by 229 (18 self)
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In this paper, we propose a new shared memory model: Transactional
LimitLESS Directories: A Scalable Cache Coherence Scheme
, 1991
"... Caches enhance the performance of multiprocessors by reducing network tra#c and average memory access latency. However, cache-based systems must address the problem of cache coherence. We propose the LimitLESS directory protocol to solve this problem. The LimitLESS scheme uses a combination of hardw ..."
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Cited by 221 (28 self)
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Caches enhance the performance of multiprocessors by reducing network tra#c and average memory access latency. However, cache-based systems must address the problem of cache coherence. We propose the LimitLESS directory protocol to solve this problem. The LimitLESS scheme uses a combination of hardware and software techniques to realize the performance of a full-map directory with the memory overhead of a limited directory. This protocol is supported by Alewife, a large-scale multiprocessor. We describe the architectural interfaces needed to implement the LimitLESS directory, and evaluate its performance through simulations of the Alewife machine.
Midway: Shared Memory Parallel Programming with Entry Consistency for Distributed Memory Multiprocessors
, 1991
"... Distributed memory multiprocessing offers a cost-effective and scalable solution for a large class of scientific and numeric applications. Unfortunately, the performance of current distributed memory programming environments suffers because the frequency of communication between processors can excee ..."
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Cited by 192 (0 self)
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Distributed memory multiprocessing offers a cost-effective and scalable solution for a large class of scientific and numeric applications. Unfortunately, the performance of current distributed memory programming environments suffers because the frequency of communication between processors can exceed that required to ensure a correctly functioning program. Midway is a shared memory parallel programming system which addresses the problem of excessive communication in a distributed memory multiprocessor. Midway programs are written using a conventional MIMD-style programming model executing within a single globally shared memory. Local memories on each processor cache recently used data to counter the effects of network latency. Midway is based on a new model of memory consistency called entry consistency. Entry consistency exploits the relationship between synchronization objects and the data which they protect. Updates to shared data are communicated between processors only when not ...
Performance Evaluation of Memory Consistency Models for Shared-Memory Multiprocessors
"... The memory consistency model supported by a multiprocessor architecture determines the amount of buffering and pipelining that may be used to hide or reduce the latency of memory accesses. Several different consistency models have been proposed. These range from sequential consistency on one end, al ..."
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Cited by 174 (10 self)
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The memory consistency model supported by a multiprocessor architecture determines the amount of buffering and pipelining that may be used to hide or reduce the latency of memory accesses. Several different consistency models have been proposed. These range from sequential consistency on one end, allowing very limited buffering, to release consistency on the other end, allowing extensive buffering and pipelining. The processor consistency and weak consistency models fall in between. The advantage of the less strict models is increased performance potential. The disadvantage is increased hardware complexity and a more complex programming model. To make an informed decision on the above tradeoff requires performance data for the various models. This paper addresses the issue of performance benefits from the above four consistency models. Our results are based on simulation studies done for three applications. The results show that in an environment where processor reads are blocking and writes are buffered, a significant performance increase is achieved from allowing reads to bypass previous writes. Pipelining of writes, which determines the rate at which writes are retired from the write buffer, is of secondary importance. As a result, we show that the sequential consistency model performs poorly relative to all other models, while the processor consistency model provides most of the benefits of the weak and release consistency models.
Two Techniques to Enhance the Performance of Memory Consistency Models
- In Proceedings of the 1991 International Conference on Parallel Processing
, 1991
"... The memory consistency model supported by a multiprocessor directly affects its performance. Thus, several attempts have been made to relax the consistency models to allow for more buffering and pipelining of memory accesses. Unfortunately, the potential increase in performance afforded by relaxing ..."
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Cited by 163 (6 self)
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The memory consistency model supported by a multiprocessor directly affects its performance. Thus, several attempts have been made to relax the consistency models to allow for more buffering and pipelining of memory accesses. Unfortunately, the potential increase in performance afforded by relaxing the consistency model is accompanied by a more complex programming model. This paper introduces two general implementation techniques that provide higher performance for all the models. The first technique involves prefetching values for accesses that are delayed due to consistency model constraints. The second technique employs speculative execution to allow the processor to proceed even though the consistency model requires the memory accesses to be delayed. When combined, the above techniques alleviate the limitations imposed by a consistency model on buffering and pipelining of memory accesses, thus significantly reducing the impact of the memory consistency model on performance. 1 Intro...
