Hi Andreas, On 19/01/14 03:06, Andreas Kloeckner wrote: > ALLOC_HOST_PTR with enqueue_map_buffer will give you page-locked memory > (and thus fast transfers) on Nvidia and AMD. You very likely do *not* > want to pass this buffer to any kernels though--just use it as a > transfer target.
Looking at the CL documentation for clEnqueueMapBuffer: The behavior of OpenCL function calls that enqueue commands that write or copy to regions of a memory object that are mapped is undefined. which is problematic as to create a persistent MPI request one needs a pointer which does not change. Hence, one would need to keep the buffer mapped at all times. However, doing so prevents one from copying to/from the buffer. (At least as far as I can discern.) I think my best bet might be to simply allocate a regular buffer on the host and hope that the MPI implementation decides to page lock it. Regards, Freddie.
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