Lecture 8 Notes

Theleftfigurerepresentsapullsituation

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Unformatted text preview: l optimal solution on the parent, the parent can pull the results from its children, or the child can push the results to parents. Normally when the parent is pulling the results from the children, each child has some local storage to save the result until the parent decided to read the result. Pulling by the parent involves polling on the state of the results from its children, which could block the parent from doing other useful work. In contrast, when the children are pushing the result to the parent, it doesn’t involve any local storage, because the child is “pushing out” the result. Though pushing by the children could cause contention problem at the parent, as the children of the parent could be all producing results, and pushing concurrently. The left figure represents a pull situation. The parent polls the children whether it have finished its computation. The red light means that the child node is still computing, the green light means that the child node is done and represents the local data, which is the optimal solution for the children. The right figure explains a push situation. Right after the child finishes its computation, it pushes the result to the parent. The child might involve any atomic computations. o Reduction synchronization scope. The synchronization between parent and child could be across an entire level of sub‐problems to amortize synchronization overhead, but such solutions require good load balancing at each level. On the other hand, the reductions could involve individual locks on each sub‐problem, which is sensitive to efficiency of atomic action implementation on a platform. o Data layout. For data locality of solving the sub‐problems, data associated with each sub‐problem should be distributed to each sub‐ problem. However, data such as parameter lookup tables should be shared among many sub‐problems to save storage, which also makes it easier to manage stored centrally. Solution (1) Find a recursive relation. If you...
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This document was uploaded on 03/17/2014 for the course CS 4800 at Northeastern.

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