On Tue, Mar 6, 2012 at 15:43, Timothy Stitt <timothy.stit...@nd.edu> wrote:
> Can anyone tell me whether it is legal to pass zero values for some of the > send count elements in an MPI_AlltoallV() call? I want to perform an > all-to-all operation but for performance reasons do not want to send data > to various ranks who don't need to receive any useful values. If it is > legal, can I assume the implementation is smart enough to not send messages > when the send count is 0? > > FYI: my tests show that AlltoallV operations with various send count > values set to 0...hangs. > This is allowed by the standard, but be warned that it is likely to perform poorly compared to what could be done with point-to-point or one-sided operations if most links are empty.
