if (rcount < size) {
XBT_WARN("MPI_allreduce_lr use default MPI_allreduce.");
Coll_allreduce_default::allreduce(sbuf, rbuf, rcount, dtype, op, comm);
if (rcount < size) {
XBT_WARN("MPI_allreduce_lr use default MPI_allreduce.");
Coll_allreduce_default::allreduce(sbuf, rbuf, rcount, dtype, op, comm);