Kokkos_WorkGraphPolicy.hpp

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#ifndef KOKKOS_WORKGRAPHPOLICY_HPP
#define KOKKOS_WORKGRAPHPOLICY_HPP
 
#include <impl/Kokkos_AnalyzePolicy.hpp>
#include <Kokkos_Crs.hpp>
 
namespace Kokkos {
namespace Impl {
 
template <class functor_type, class execution_space, class... policy_args>
class WorkGraphExec;
 
}
}  // namespace Kokkos
 
namespace Kokkos {
 
template <class... Properties>
class WorkGraphPolicy : public Kokkos::Impl::PolicyTraits<Properties...> {
 public:
  using execution_policy = WorkGraphPolicy<Properties...>;
  using self_type        = WorkGraphPolicy<Properties...>;
  using traits           = Kokkos::Impl::PolicyTraits<Properties...>;
  using index_type       = typename traits::index_type;
  using member_type      = index_type;
  using execution_space  = typename traits::execution_space;
  using memory_space     = typename execution_space::memory_space;
  using graph_type = Kokkos::Crs<index_type, execution_space, void, index_type>;
 
  enum : std::int32_t {
    END_TOKEN       = -1,
    BEGIN_TOKEN     = -2,
    COMPLETED_TOKEN = -3
  };
 
 private:
  using ints_type = Kokkos::View<std::int32_t*, memory_space>;
 
  // Let N = m_graph.numRows(), the total work
  // m_queue[  0 ..   N-1] = the ready queue
  // m_queue[  N .. 2*N-1] = the waiting queue counts
  // m_queue[2*N .. 2*N+2] = the ready queue hints
 
  graph_type const m_graph;
  ints_type m_queue;
 
  KOKKOS_INLINE_FUNCTION
  void push_work(const std::int32_t w) const noexcept {
    const std::int32_t N = m_graph.numRows();
 
    std::int32_t volatile* const ready_queue = &m_queue[0];
    std::int32_t volatile* const end_hint    = &m_queue[2 * N + 1];
 
    // Push work to end of queue
    const std::int32_t j = atomic_fetch_add(end_hint, 1);
 
    if ((N <= j) || (END_TOKEN != atomic_exchange(ready_queue + j, w))) {
      // ERROR: past the end of queue or did not replace END_TOKEN
      Kokkos::abort("WorkGraphPolicy push_work error");
    }
 
    memory_fence();
  }
 
 public:
  KOKKOS_INLINE_FUNCTION
  std::int32_t pop_work() const noexcept {
    const std::int32_t N = m_graph.numRows();
 
    std::int32_t volatile* const ready_queue = &m_queue[0];
    std::int32_t volatile* const begin_hint  = &m_queue[2 * N];
 
    // begin hint is guaranteed to be less than or equal to
    // actual begin location in the queue.
 
    for (std::int32_t i = *begin_hint; i < N; ++i) {
      const std::int32_t w = ready_queue[i];
 
      if (w == END_TOKEN) {
        return END_TOKEN;
      }
 
      if ((w != BEGIN_TOKEN) &&
          (w == atomic_compare_exchange(ready_queue + i, w,
                                        (std::int32_t)BEGIN_TOKEN))) {
        // Attempt to claim ready work index succeeded,
        // update the hint and return work index
        atomic_increment(begin_hint);
        return w;
      }
      // arrive here when ready_queue[i] == BEGIN_TOKEN
    }
 
    return COMPLETED_TOKEN;
  }
 
  KOKKOS_INLINE_FUNCTION
  void completed_work(std::int32_t w) const noexcept {
    Kokkos::memory_fence();
 
    // Make sure the completed work function's memory accesses are flushed.
 
    const std::int32_t N = m_graph.numRows();
 
    std::int32_t volatile* const count_queue = &m_queue[N];
 
    const std::int32_t B = m_graph.row_map(w);
    const std::int32_t E = m_graph.row_map(w + 1);
 
    for (std::int32_t i = B; i < E; ++i) {
      const std::int32_t j = m_graph.entries(i);
      if (1 == atomic_fetch_add(count_queue + j, -1)) {
        push_work(j);
      }
    }
  }
 
  struct TagInit {};
  struct TagCount {};
  struct TagReady {};
 
  KOKKOS_INLINE_FUNCTION
  void operator()(const TagInit, int i) const noexcept {
    m_queue[i] = i < m_graph.numRows() ? END_TOKEN : 0;
  }
 
  KOKKOS_INLINE_FUNCTION
  void operator()(const TagCount, int i) const noexcept {
    std::int32_t volatile* const count_queue = &m_queue[m_graph.numRows()];
 
    atomic_increment(count_queue + m_graph.entries[i]);
  }
 
  KOKKOS_INLINE_FUNCTION
  void operator()(const TagReady, int w) const noexcept {
    std::int32_t const* const count_queue = &m_queue[m_graph.numRows()];
 
    if (0 == count_queue[w]) push_work(w);
  }
 
  execution_space space() const { return execution_space(); }
 
  WorkGraphPolicy(const graph_type& arg_graph)
      : m_graph(arg_graph),
        m_queue(view_alloc("queue", WithoutInitializing),
                arg_graph.numRows() * 2 + 2) {
    {  // Initialize
      using policy_type  = RangePolicy<std::int32_t, execution_space, TagInit>;
      using closure_type = Kokkos::Impl::ParallelFor<self_type, policy_type>;
      const closure_type closure(*this, policy_type(0, m_queue.size()));
      closure.execute();
      execution_space().fence();
    }
 
    {  // execute-after counts
      using policy_type  = RangePolicy<std::int32_t, execution_space, TagCount>;
      using closure_type = Kokkos::Impl::ParallelFor<self_type, policy_type>;
      const closure_type closure(*this, policy_type(0, m_graph.entries.size()));
      closure.execute();
      execution_space().fence();
    }
 
    {  // Scheduling ready tasks
      using policy_type  = RangePolicy<std::int32_t, execution_space, TagReady>;
      using closure_type = Kokkos::Impl::ParallelFor<self_type, policy_type>;
      const closure_type closure(*this, policy_type(0, m_graph.numRows()));
      closure.execute();
      execution_space().fence();
    }
  }
};
 
}  // namespace Kokkos
 
#ifdef KOKKOS_ENABLE_SERIAL
#include "impl/Kokkos_Serial_WorkGraphPolicy.hpp"
#endif
 
#ifdef KOKKOS_ENABLE_OPENMP
#include "OpenMP/Kokkos_OpenMP_WorkGraphPolicy.hpp"
#endif
 
#ifdef KOKKOS_ENABLE_CUDA
#include "Cuda/Kokkos_Cuda_WorkGraphPolicy.hpp"
#endif
 
#ifdef KOKKOS_ENABLE_HIP
#include "HIP/Kokkos_HIP_WorkGraphPolicy.hpp"
#endif
 
#ifdef KOKKOS_ENABLE_THREADS
#include "Threads/Kokkos_Threads_WorkGraphPolicy.hpp"
#endif
 
#ifdef KOKKOS_ENABLE_HPX
#include "HPX/Kokkos_HPX_WorkGraphPolicy.hpp"
#endif
 
#endif /* #define KOKKOS_WORKGRAPHPOLICY_HPP */