| 12 | | === What is CUDA-awareness for MPI? === |
| 13 | | In brief, ''CUDA-awareness'' in an MPI library means that a mixed CUDA + MPI application is allowed to pass pointers to CUDA buffers (these are memory regions located on the GPU, the so-called ''Device'' memory) directly to MPI functions like `MPI_Send` or `MPI_Recv`. A non CUDA-aware MPI library would fail in such a case because the CUDA-memory cannot be accessed directly e.g. via load/store or `memcpy()` but has previously to be transferred via special routines like `cudaMemcpy()` to the Host memory. In contrast to this, a CUDA-aware MPI library recognizes that a pointer is associated with a buffer within the Device memory and can then copy this buffer before communication temporarily into the Host memory -- what is called ''Staging'' of this buffer. In addition, a CUDA-aware MPI library may also apply some kind of optimizations, for example, by means of exploiting so-called ''GPUDirect'' capabilities that allow for direct RDMA transfers from and to Device memory. |
| | 12 | === What is CUDA awareness for MPI? === |
| | 13 | In brief, ''CUDA awareness'' in an MPI library means that a mixed CUDA + MPI application is allowed to pass pointers to CUDA buffers (these are memory regions located on the GPU, the so-called ''Device'' memory) directly to MPI functions such as `MPI_Send()` or `MPI_Recv()`. A non CUDA-aware MPI library would fail in such a case because the CUDA-memory cannot be accessed directly, e.g., via load/store or `memcpy()` but has to be transferred in advance to the host memory via special routines such as `cudaMemcpy()`. As opposed to this, a CUDA-aware MPI library recognizes that a pointer is associated with a buffer within the device memory and can then copy this buffer prior to the communication into a temporarily host buffer -- what is called ''staging'' of this buffer. Additionally, a CUDA-aware MPI library may also apply some kind of optimizations, e.g., by means of exploiting so-called ''GPUDirect'' capabilities that allow for direct RDMA transfers from and to the device memory. |
