Hi, MPI_Allreduce offers the possibility to use the same buffer for the send and recv data: http://www.open-mpi.org/doc/v1.4/man3/MPI_Allreduce.3.php#toc8 It seems that boost's all_reduce does not allow such a feature. First, I would like to know if the previous statement is correct and, if yes, if it was just overlooked or if there was a reason for that? Just in case, I filed a ticket regarding that issue, along with a tentative patch, in https://svn.boost.org/trac/boost/ticket/6704 Regards, Alain