High-performance data transfer (HPDT)

High-performance data transfer (HPDT) optimizes the performance of large data transfers for VTAM® LU 6.2 applications. The performance benefits provided by HPDT services are achieved by more efficient use of critical CPU resources (CPU cycles, cache, memory bus, and the channel). Specifically, system resources are conserved by the following methods:

Reduction of VTAM internal data copies:: The movement of large pieces of data can result in significant processing costs on the send and receive execution paths. This cost is because of the effective path length of the MVCL instruction. Additionally, data movement flushes the CPU cache and consumes the memory bus bandwidth.
Reduced path length:: The processing of data transfers is streamlined through the use of the communications storage manager (CSM), which reduces the increase in path length that normally occurs as API crossing and PIU size increase. CSM is described in Communications storage manager.
Use of HPDT MPC:: HPDT services take advantage of HPDT MPC, which is described in Multipath channel connections.

HPDT includes a service that reduces the number of times data is moved for an APPCCMD send or receive request. No application change is required to receive performance benefits. However, an HPDT interface is also provided to enable applications to obtain performance benefits even greater than those provided by HPDT services. For more information about the HPDT interface, see z/OS Communications Server: SNA Programmer's LU 6.2 Guide.

Applications using the HPDT interface can specify CSM data space or CSM extended common service area (ECSA) for inbound data. When CSM data space is specified, the storage, when fixed, tends to be backed by real storage on or above the 2-gigabyte bar. VTAM receives data over the channel in the storage type specified by the STORAGE operand on the TRLE definition statement. If a mismatch exists between the VTAM TRLE definition and the application specification, an extra data move occurs. You should consider the CSM storage type used by your LU 6.2 applications when setting the STORAGE parameter for the TRLE definition. For more information about the TRLE definition, see z/OS Communications Server: SNA Resource Definition Reference.