1. A rack server system for a map/reduce data processing, comprising: a plurality of servers arranged in a rack, and a plurality of offload processor modules supported on at least two of the servers, each offload processor module having an input-output (IO) port and multiple offload processors, a first offload processor module configured to execute map steps of the map/reduce data processing, and being connected directly to a second offload processor through their respective IO ports to define a midplane switch, wherein a second offload processor module is configured to execute reduce steps of the map/reduce data processing on data provided from the first offload processor module, and the first offload processor module is configured to generate virtual interrupts corresponding to the execution of the map steps.