A system includes an input/output adapter that includes a multi-source selector coupled to a flow-through input, an elastic first-in-first-out (FIFO) structure, a completion queue, and an output bus. A controller is operatively connected to the input/output adapter. The controller is operable to select the flow-through input to pass through the multi-source selector to the output bus based on determining that the elastic FIFO structure is empty. The elastic FIFO structure is selected to pass through the multi-source selector to the output bus based on determining that the elastic FIFO structure includes at least one entry. The completion queue is selected to pass through the multi-source selector to the output bus based on determining that the completion queue includes at least one entry. The flow-through input is routed into the elastic FIFO structure based on the completion queue being selected to pass through the multi-source selector to the output bus.