Method and apparatus for selectively using input/output buffers as a retransmit vehicle in an information handling system

Abstract

A method and apparatus for selectively using input/output (I/O) buffers as a retransmit vehicle in a client/server system. The decision whether to use an I/O buffer as a retransmit vehicle is based on a number of factors, including the packet size, the expected round-trip time (RTT) for an acknowledgment of the transmission, the number of I/O buffers currently allocated, and the number of I/O buffers remaining. If the decision is made not to use the I/O buffer as a retransmit vehicle, then the data is copied into a send buffer that is maintained by the system for the particular requester. Initially three threshold values, the round-trip time (RTT) threshold, the critical threshold, and the tight buffer threshold, are set. Connections having a longer round-trip time than a set round-trip time threshold or connections made when the number of I/O buffers remaining is below the critical threshold are not allowed to keep the I/O buffer as a retransmission vehicle. If the number of I/O buffers remaining falls below the critical threshold, a critical stabilization interval is started. During a critical stabilization interval, the I/O buffers may not be used as a retransmit vehicle if the number of I/O buffers already allocated exceeds the tight buffer threshold, even if the number of I/O buffers remaining is above the critical threshold. For each I/O buffer, a use count is maintained of the number of packets in the buffer awaiting acknowledgment. The use count is decremented each time an acknowledgment is received for one of the packets in the I/O buffer. When the use count has been decremented to zero, the I/O buffer is freed.