An information processing system includes a first processor that issues a first write request group including a plurality of data write requests for writing first data to a memory. The first processor issues a first completion write request after issuing the first write request group. The first completion write request is a request for writing completion information to the memory. The completion information indicates completion of write processing requested by the first write request group. The first processor inserts a first barrier instruction into the issued requests, between the first write request group and the first completion write request. The first processor outputs all of the plurality of data write requests included in the first write request group, subsequently outputs the first barrier instruction, and subsequently outputs the first completion write request.