Embodiments of this application provide a method, includes: receiving a first data flow that includes a plurality of data units; inputting N1 data units of the plurality of data units and a first source marking unit into the first source queue; inputting M1 data units of the plurality of data units and a first target marking unit into the first target queue, wherein the N1 data units and the M1 data units are different data units; scheduling the N1 data units and the first source marking unit based on the first source marking unit and the first target marking unit; and scheduling the first target marking unit and the M1 data units, wherein the first target marking unit and the M1 data units are scheduled later than the N1 data units and the first source marking unit are scheduled.