High performance data transfer (HPDT) optimizes the performance of large message transfers (sending and receiving operations) for VTAM® LU 6.2 applications. No application change is required to obtain HPDT services. When an LU 6.2 application issues an APPCCMD send or receive request, HPDT services are invoked automatically if the session is bound over a connection that supports channel I/O operations using buffers in the communications storage manager (CSM). These connections are explained in the z/OS Communications Server: SNA Network Implementation Guide. HPDT services are also available for data transfers between two LU 6.2 applications that reside on the same host. HPDT increases total system throughput by reducing the requirements on system resources (CPU, memory bus, effective pathlength, and cache) and thereby increasing the total number of streams that can be supported by a CPU with given MIPS (one million instructions per second) capacity, memory bus bandwidth, and configuration limits.

This chapter describes an HPDT interface that applications can use for obtaining performance benefits even greater than when HPDT services are available for normal APPCCMD send and receive requests. The HPDT interface includes an API for using CSM (IVTCSM macroinstruction) and an extension to the APPCCMD macroinstruction (OPTCD=XBUFLST). Optimal performance is achieved by using the HPDT interface to eliminate the data copy at the APPCCMD interface.