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Performance Comparison of Processor Allocation Algorithms

Taghdimi Abbas Pour, Majid | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39730 (19)
  4. University: Sharif University of Technology
  5. Department: Computer Engineering
  6. Advisor(s): Sarbazi Azad, Hamid
  7. Abstract:
  8. Efficient processor allocation and job scheduling algorithms are critical if the full computational power of large-scale multicomputers is to be harnessed effectively. Processor allocation is responsible for selecting the set of processors on which parallel jobs are executed, whereas job scheduling is responsible for determining the order in which the jobs are executed. Many processor allocation strategies have been devised for mesh-connected multicomputers and these can be divided into two main categories: contiguous and non-contiguous. In contiguous allocation, jobs are allocated distinct contiguous processor submeshes for the duration of their execution. Such a strategy could lead to high processor fragmentation which degrades system performance in terms of, for example, the turnaround time and system utilisation. In non-contiguous allocation, a job can execute on multiple disjoint smaller sub-meshes rather than waiting until a single sub-mesh of the requested size and shape is available. Although non-contiguous allocation increases message contention inside the network, lifting the contiguity condition can reduce processor fragmentation and increase system utilisation. The first part of the research presents a new contiguous allocation strategy, referred to as Turning Recursive-based Allocation (TRA), for 3D mesh-connected multicomputers. The TRA strategy considers only those available free sub-meshes which border from the left of those already allocated sub-meshes or which have their left boundaries aligned with that of the whole mesh network. Moreover TRA uses an efficient scheme to facilitate the detection of such available sub-meshes while maintaining a low allocation overhead. This is achieved through maintaining a list of allocated sub-meshes in order to efficiently determine the processors that can form an allocation sub-mesh for a new allocation request. The new strategy is able to identify a free sub-mesh of the requested size as long as it exists in the mesh. Results from extensive simulations under various operating loads reveal that TRA manages to deliver competitive performance (i.e., low turnaround times and high system utilisation) with a much lower allocation overhead compared to other well-known existing strategies. Most existing non-contiguous allocation strategies that have been suggested for the mesh suffer from several problems that include internal fragmentation, external fragmentation, and message contention inside the network. Furthermore, the allocation of processors to job requests is not based on free contiguous sub-meshes in these existing strategies. The second part of this research proposes a new non-contiguous allocation strategy, referred to as Quick Recursive-based Noncontiguous Allocation (QRNA) strategy that eliminates both internal and external fragmentation and alleviates the contention in the network. QRNA combines the desirable features of both contiguous and non-contiguous allocation strategies as it adopts the contiguous allocation used in our TRA strategy. Moreover, QRNA is flexible enough in that it could be applied to either the 2D or 3D mesh. However, for the sake of the present study, the new non-contiguous allocation strategy is discussed for the 2D mesh and compares its performance against that of well-known non-contiguous allocation strategies suggested for this network. One of the desirable features of QRNA is that it can maintain a high degree of contiguity between processors compared to the previous allocation strategies. This, in turn, decreases the number of sub-meshes allocated to a job, and thus decreases message distances, resulting in a low inter-processor communication overhead. The performance analysis here indicates that the new proposed strategy has lower turnaround time than the previous non-contiguous allocation strategies for most considered cases. Moreover, in the presence of high message contention due to heavy network traffic, QRNA exhibits superior performance in terms of the turnaround time over the previous contiguous and noncontiguous allocation strategies. Furthermore, QRNA exhibits a high system utilisation as it manages to eliminate both internal and external fragmentation.


  9. Keywords:
  10. Scattering ; Mesh Network ; Multicomputer System ; Processor Allocation ; Contiguous Allocation Algorithm ; Non-Contiguous Allocation Algorithm

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