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SYCL: Make sure to use a large enough workgroup size for tree traversal #931

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SYCL: Make sure to use a large enough workgroup size for tree traversal #931

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12 changes: 8 additions & 4 deletions src/details/ArborX_DetailsTreeTraversal.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -62,10 +62,14 @@ struct TreeTraversal<BVH, Predicates, Callback, SpatialPredicateTag>
}
else
{
Kokkos::parallel_for("ArborX::TreeTraversal::spatial",
Kokkos::RangePolicy<ExecutionSpace>(
space, 0, Access::size(predicates)),
*this);
Kokkos::RangePolicy<ExecutionSpace> policy(space, 0,
Access::size(predicates));
// FIXME_SYCL
#ifdef KOKKOS_ENABLE_SYCL
if constexpr (std::is_same_v<ExecutionSpace, Kokkos::Experimental::SYCL>)
policy.set_chunk_size(1024);
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Can you please add a comment on the considerations that went into choosing 1024?

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Not quite sure if there is much behind it rather than that choosing the maximum gave much better performance (than 32 which is what the compiler chose) and I couldn't find a different workgroup size that gave better results (but results don't differ much choosing between 256 and 1024 threads per workgroup).

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Can you please post the results in this issue for different workgroup sizes?

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I'll share it privately.

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@dalg24 dalg24 Aug 23, 2023 •
edited
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Please cc me

#endif
Kokkos::parallel_for("ArborX::TreeTraversal::spatial", policy, *this);
}
}

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