In the z/OS environment, the IOSDRIVR option can be used instead of EXCP or EXCPVR. The IOSDRIVR option directs the z/OS TDP to call IOS directly through the STARTIO macro interface to request that I/O be done on its behalf. To make TDP invoke the IOS driver routine (TDPIODVR) instead of invoking EXCP or EXCPVR, In the TDPPARM data set, include the TDP INITIAL command:
INITIAL IOMODE IOSDRIVR
In a heavily loaded TDP, the IOSDRIVR option can reduce CPU utilization when compared to EXCP or EXCPVR. Also, where TDP I/O queue lengths are consistently greater than 0, the I/O path lengths can be reduced because the disabled interrupt exit (DIE) will fetch the next I/O request and submit it to IOS. Whenever the I/O completes successfully, post status processing (back-end IOS) also is avoided.
Since the TDP address space is nonswappable, and the I/O related control blocks are in fixed storage, Teradata Database-bound I/O will be re-driven out of any address space. That is, this occurs wherever the I/O interrupt is fielded for the previous I/O, thus avoiding address-space swapping to handle the interrupt and subsequent re-drive of new I/O.