Buffers.hpp

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//
// Buffers.hpp
//   Interface for globally accessible buffer factory for communication
//
//   Data sent between MPI ranks has to be stored in a buffer for sending and receiving.
//   To reduce the number of times memory has to be allocated and freed, the buffer
//   factory interface allows buffers to be reused. This is especially relevant on
//   GPUs, as Cuda allocation calls are expensive. To avoid reallocating the buffers
//   in the case that the amount of data to be exchanged increases, when a new buffer
//   is created, an amount of memory greater than the requested size is allocated
//   for the new buffer. The factor by which memory is overallocated is determined by
//   a data member in Communicator, which can be set and queried at runtime. Only new
//   buffers are overallocated. If a buffer is requested with the same ID as a buffer
//   that has been previously allocated, the same buffer will be used. If the requested
//   size exceeds the buffer size, that buffer will be resized to have exactly
//   the requested size.
//
//   Currently, the buffer factory is used for application of periodic boundary
//   conditions; halo cell exchange along faces, edges, and vertices; as well as
//   exchanging particle data between ranks.
//
 
namespace ippl {
    namespace mpi {
 
        template <typename MemorySpace, typename T>
        Communicator::buffer_type<MemorySpace> Communicator::getBuffer(size_type size,
                                                                       double overallocation) {
            auto& buffer_handler = buffer_handlers_m.get<MemorySpace>();
 
            return buffer_handler.getBuffer(size * sizeof(T),
                                            std::max(overallocation, defaultOveralloc_m));
        }
 
        template <typename MemorySpace>
        void Communicator::freeBuffer(Communicator::buffer_type<MemorySpace> buffer) {
            auto& buffer_handler = buffer_handlers_m.get<MemorySpace>();
 
            buffer_handler.freeBuffer(buffer);
        }
 
    }  // namespace mpi
 
}  // namespace ippl