Data stream prefetch optimization

The data stream prefetch optimization is available only in POWER7 processors. The data stream prefetch optimization is a feature of the IBM®AIX® Dynamic System Optimizer that modifies the Data Stream Control Register (DSCR), when required, to improve the performance of an application.

A system that is based on the IBM Power Architecture® implementation includes a special purpose register named the DSCR. The DSCR controls the enablement, depth, and settings for hardware data stream prefetching. This setting is correct when the DSCR maximizes the amount of information that it is able to access in the shortest amount of time. The prefetch optimization accomplishes this performance by loading some data that is frequently accessed before that data is required, based on established patterns.

This optimization often benefits systems that have large memory footprints and high processor utilization with high context switch rates. When enabled, the Active System Optimizer collects information from the AIX kernel and Performance Monitoring Unit (PMU) to dynamically determine the optimal setting for this register for a specific application.