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–
Mid-project status
reports will be
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week of Nov 1
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Schedule
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Oct
‐
10
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CS6230 – HPC Tools and Applications
Reductions and Parallel Prefix Sum
Jeffrey S. Vetter
Computational Science and Engineering
College of Computing
Georgia Institute of Technology
http://ft.ornl.gov/~vetter
[email protected]

EXAMPLE: REDUCTIONS
Borrowed from David Kirk/NVIDIA, Wen
‐
mei W. Hwu, and John Stratton, 2007
‐
2009
ECE 498AL, University of Illinois, Urbana
‐
Champaign
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Parallel Reductions
•
Simple array reductions reduce all of the data in an array to a
single value that contains some information from the entire array.
–
Sum, maximum element, minimum element, etc.
•
Used in lots of applications, although not always in parallel form
–
Matrix Multiplication is essentially performing a sum reduction over the
element
‐
product of two vectors for each output element: but the sum is
computed by a single thread
•
Assumes that the operator used in the reduction is associative
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Technically not true for things like addition on floating
‐
point numbers, but
it’s common to pretend that it is