Add a helper function for "for each element loop" #170

makortel · 2021-02-02T17:21:06Z

From https://github.com/cms-patatrack/pixeltrack-standalone/pull/165/files#r565486352

A pattern

const auto gridDim = ...;
const auto [firstNoStride, endNoStride] = ...;
for (auto threadIdx = firstNoStride, endElementIdx = endNoStride; threadIdx < MAX; threadIdx += gridDimension, endElementIdx += gridDimension) {
  for (auto i = threadIdx; i < std::min(endElementIdx, MAX); ++i ) {
    <body>
  }
}

seems to repeat often. The pattern could be abstracted along

namespace cms::alpakatools {
  // the name should be more descriptive...
  template <typename T_Acc, typename N, typename Func>
  inline void for_each_element(const T_Acc& acc, const N nitems, Func func) {
    const auto gridDim = ...;
    const auto [firstNoStride, endNoStride] = ...;
    for (auto threadIdx = firstNoStride, endElementIdx = endNoStride; threadIdx < nitems; threadIdx += gridDimension, endElementIdx += gridDimension) {
      for (auto i = threadIdx; i < std::min(endElementIdx, nitems); ++i ) {
        func(i);
      }
    }
  }
}

that could be called along

const uint32_t nt = offsets[nh];
cms::alpakatools::for_each_element(acc, nt, [&](uint32_t i) {
  auto off = alpaka_std::upper_bound(offsets, offsets + nh + 1, i);
  ...
}

makortel added the alpaka label Feb 2, 2021

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Add a helper function for "for each element loop" #170

Add a helper function for "for each element loop" #170

makortel commented Feb 2, 2021

Add a helper function for "for each element loop" #170

Add a helper function for "for each element loop" #170

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makortel commented Feb 2, 2021