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In time 1 n memory readwrite collisions must be

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Unformatted text preview: mance •  more portable; leave low-level details to the compiler NAS MG: Operational View •  Data structures: –  3D arrays & 3D hierarchical arrays (2D in my pictures) –  3D sparse arrays can also be useful •  4 primary kernels: –  each computed using 27-point stencils •  •  •  •  resid: compute residual psinv: compute approximate inverse rprj3: projection from fine grid to coarse interp: interpolation from coarse grid to fine –  periodic boundary conditions •  computation of approximate norms –  norm2u3: approximate L2 & uniform norms •  initialization, output NAS MG: Parallel Implementation •  Arrays typically use block distributions –  good load balance (computation is homogenous) –  ghost cells allocated for caching neighbors’ values •  Communication Idioms: –  4 kernels require point-to-point communication –  toroidal communication required for boundaries –  global reductions required to compute norms –  reductions useful during initialization as well Q: In a Shared- Memory seXng, which would you use from the perspec3ve of memory? Reduces opportunity for false sharing CSEP 524: Parallel ComputaIon Winter 2013: Chamberlain 53 Q: In the seXng of MG, which would you use? Best surface to volume raIo (good for stencil computaIons) CSEP 524: Parallel ComputaIon Winter 2013:...
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