Hot Spot Contention Research Articles

Modeling the effect of hot spot contention on crossbar multiprocessors

The paper models the performance characteristics of crossbar multiprocessors under hot spot contention. The effect of hot spot contention in previous works was under-estimated because the blocked requests were assumed to be discarded. The model in the paper provides more accurate results by taking into account the retransmission of blocked requests.

Reducing hot-spot contention in shared-memory multiprocessor systems

In shared-memory multiprocessor systems that use multistage interconnection networks, memory contention can produce "tree saturation", which ultimately degrades system performance. This article categorizes, reviews, and compares existing strategies for reducing these effects.

A circular list based mutual exclusion scheme for large shared-memory multiprocessors

Mutual exclusion in shared-memory multiprocessors is realized by employing a lock to determine the processor among those which compete for the critical section. Accesses to such a mutual exclusion lock may create heavy synchronization traffic and/or serious contention over the network, thereby degrading system performance considerably. In this paper, we introduce an efficient scheme which keeps synchronization traffic low and avoids serious hot-spot contention. This is made possible by constructing a circular list of the processors waiting for the critical section and by dispersing accesses to the lock. Extensive simulation of the proposed approach was conducted and the lower bound on the elapsed time was derived. Our simulation results demonstrate that the proposed scheme indeed achieves better performance than prior techniques, with its elapsed time close to the lower bound for the whole range of simulated system sizes, thus promising good scalability for large systems.

A Fault-Tolerant Multistage Combining Network

In this paper, we propose a solution to both fault tolerance and hot-spot contention problems in multiprocessor systems with multistage interconnection networks. Combining networks are known to be effective in handling hot-spot traffic. However, the fault tolerance capability of unique-path combining network is insufficient and must be enhanced. Thus, we use the chaining scheme, which provides alternate routing paths by connecting intrastage switching elements with a chain, to enhance the fault tolerance capability of combining network. As a result, we propose a chained combining network. Because of the bidirectionality of combining networks, we also develop routing procedures for the chained combining network. With slight modifications, these routing procedures can also be used in other multipath fault-tolerant combining networks.

An analysis of the hot spot contention and message combining on the simple serial synchronized‐multistage interconnection network

AbstractSimple serial synchronized (SSS) multistage interconnection network (MIN) is a processor‐memory connection network that has a high performance/cost ratio, where the packet is inputted and switch synchronously in the MIN, which has a high pass‐through ratio and is composed of simple elements. This paper evaluates the effect of the hot spot contention and the effect of the synchronous bit‐serial (SBS) message combining in SSS‐MIN, by the theoretical analysis based on probability and simulation. In contrast to conventional MIN, there does not arise a complete tree saturation in SSS‐MIN, but an area, to which the access is difficult, is produced according to the relative position to the hot spot contention. From such a viewpoint, an analysis method for the pass‐through ratio is presented, which considers the position of the switching element to the hot spot. It is verified as a result of evaluation that the proposed method of analysis gives a result close to that of simulation, so long as the access to the hot spot and the connection network architecture stay within a practical range. It is also seen that the pass‐through ratio is deteriorated less in SSS‐MIN by the hot spot contention than in the conventional MIN, and the effect can be almost completely eliminated by the SBS message combining. When a multiprocessor system is actually constructed, performance deterioration due to hot spot contention is greater than in the case where only the pass‐through ratio is considered. This can also be eliminated almost completely by the SBS message combining.

Comparative performance evaluation of hot spot contention between MIN-based and ring-based shared-memory architectures

Hot spot contention on a network-based shared-memory architecture occurs when a large number of processors try to access a globally shared variable across the network. While multistage interconnection network (MIN) and hierarchical ring (HR) structures are two important bases on which to build large scale shared-memory multiprocessors, the different interconnection networks and cache/memory systems of the two architectures respond very differently to network bottleneck situations. In this paper, we present a comparative performance evaluation of hot spot effects on the MIN-based and HR-based shared-memory architectures. Both nonblocking MIN-based and HR-based architectures are classified, and analytical models are described for understanding network differences and for evaluating hot spot performance on both architectures. The analytical comparisons indicate that HR-based architectures have the potential to handle various contentions caused by hot spots more efficiently than MIN-based architectures. Intensive performance measurements on hot spots have been conducted on the BBN TC2000 (MIN-based) and the KSR1 (HR-based) machines. Performance experiments were also conducted on the practical experience of hot spots with respect to synchronization lock algorithms. The experimental results are consistent with the analytical models, and present practical observations and an evaluation of hot spots on the two types of architectures.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Hot-spot contention in binary hypercube networks

Consideration is given to the impact of hot-spot contention in distributed-memory multicomputer systems. Since the binary hypercube network offers a reasonable compromise between network cost and performance, two hypercube-based static interconnection networks are considered. One is a standard binary hypercube and the other is a binary hypercube-based hierarchical interconnection network. The impact of hot-spot contention in both these networks is studied. >

A cost-effective combining structure for large-scale shared-memory multiprocessors

A cost-effective combining structure to alleviate hot-spot contention is proposed. The key idea is that the combining function is separated from the routing function, so that a binary tree-based combining configuration becomes feasible. The combining element for realizing the new structure has only one wait buffer and one combining logic, involving less hardware than the element used in earlier combining networks. More importantly, the number of constituent combining elements in such a structure with size N is reduced to O(1/log/sub 2/ N) of that required in the previous design. The proposed combining structure in conjunction with a regular multistage interconnection network can remove hot-spot contention effectively in any sized system at a considerably lower cost, and appears readily suitable for use in some applications. >

Rearrangeable switch fabric for fast packet switching

The knockout switch is a switch fabric proposed for fast packet switching. Under certain non-uniform traffic patterns (i.e. a ‘hot spot contention’) the switch exhibits an increase in the packet loss rate. A rearrangeable switch fabric based on knockout switch concepts is proposed which, on the occurrence of ‘hot spot’ traffic, reconfigures itself to guarantee a very low packet loss rate. The new switch architecture is presented, and parameters affecting performance are analysed. An implementation based on dynamically reconfigurable VLSI components is proposed.

On hot-spot contention in interconnection networks

A major component of a parallel machine is its interconnection network, which provides concurrent communication between the processing elements. It is common to use a multi-stage interconnection network (MIN) which is constructed using crossbar switches and introduces not only contention for destination addresses but also additional contention for internal switches. Both types of contention are increased when non-local communication across a MIN becomes concentrated on a certain destination address, for example when a frequently-accessed data structure is stored entirely in one element of a distributed memory. Such an address, often called a hot-spot , affects the blocking probability of paths to other destination addresses because of the shared internal switches. This paper describes an analytical model of hot-spot contention and quantifies its effect on the performance of a MIN with a circuit switching communication protocol. We obtain performance measures for a MIN in which partial paths are held during path building and one destination address is more frequently chosen by incoming traffic than other addresses.

On “hot spot” contention

In a recent paper. Pfister and Norton[4] brought to our attention the potential degradation in performance of multi-stage interconnection networks in the presence of nonuniform traffic patterns. More specifically, they studied the effect of a single hot spot - a location that is accessed more frequently - in an otherwise uniform traffic environment. Their simulations assumed that all input lines contribute to the hot spot. Their results showed that the effect of hot spots drastically reduced the bandwidth of the network. In this note. we confirm Pfister and Norton's results and present supplemental data and arguments which illustrate other aspects of hot spot contention. In particular, we show that the performance improves when the source of the hot spot is more localized.