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Subject: H5Part development and discussion

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Re: [H5part] Re: H5Block and ghost zones

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  • From: Mark Howison <MHowison AT>
  • To: Andreas Adelmann <andreas.adelmann AT>
  • Cc: Achim Gsell <Achim.Gsell AT>, h5part AT, John Shalf <JShalf AT>
  • Subject: Re: [H5part] Re: H5Block and ghost zones
  • Date: Tue, 13 Jul 2010 15:46:25 -0700
  • List-archive: <>
  • List-id: H5Part development and discussion <>

Hi Andreas,

It means you can have different depths of ghost cells on different
sides of the 3D block. So the top might have +1 ghost cells, but the
sides +2, etc. Adjacent blocks with ghost zones also overlap, and it
is fairly complicated to "reduce" these into non-overlapping regions.
Right now we handle the most general case, where we don't require any
adjacency information from the user. There is an MPI_Allgather where
each processor gets a copy of every other proc's field layout,
requiring O(n) space. Then an O(n^2) algorithm runs redundantly on
each proc to compute the reduction,

It all works and I have never noticed any performance issues
associated with it, but it may become a scalability problem in the
future with say O(100K) or O(1M) cores.


On Sat, Jul 10, 2010 at 9:23 AM, Andreas Adelmann
<andreas.adelmann AT> wrote:
>>> Do we need to support arbitrary ghost zones?
> Sorry I was maybe not following closely: what are rbitrary ghost zones
> w.r.t. H5Block?
> AA

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