APAR PJ42459 provides support for the enhanced-DAT facility 2 (EDAT-2). During dynamic-address translation, EDAT-2 allows a region-third-table entry to specify the absolute storage location of a 2G-byte block instead of a segment-table origin. When DAT tables are set up to use EDAT-2, system performance may be improved due to a significant reduction in the number of TLB entries used for translation of addresses in the 2G-byte block, thus allowing the TLB entries to be used to translate other addresses.
When PJ42459 is applied, the storage-initialization CSECT, CCCTIN, defines an EDAT-only point. Once the EDAT-only point has been reached, all subsequent storage allocations are made using EDAT-2 if available, or EDAT-1 if EDAT-2 is not available. (EDAT-1 uses 1M-byte frames instead of 2G-byte frames.) The storage areas allocated in the EDAT-only area are:
- ECB macro trace
- ECB heap trace
- ECB resource manager RLT and RCT
- OSA read buffers
- Name-value pair area
- VFA
APAR PJ42459 can be applied to any processor that is currently supported by z/TPF; today that includes z10 processors and later. However, in order to exploit the support (that is, use 2G-byte frames to back the EDAT-only area), a native zEC12 or later is required. If the customer is on a z10, z196, or z114 then only EDAT-1 (1M-byte) frames are used in the EDAT-only area.
It is important to note that when running on a test system that is a guest under VM, neither EDAT-1 nor EDAT-2 is available, even on a zEC12 or z13. As a result, only 4K-byte frames are used to back the EDAT-only area.