Contents | Previous | Next

Performance Improvements

The following items improve performance.

  • CP 64-Bit Support
  • VCTC Pathlength Reduction
  • Miscellaneous CMS Improvements
  • Gigabit Ethernet Support via QDIO

CP 64-Bit Support

The support provided in z/VM 3.1.0 for virtual machine sizes larger than 2 Gigabytes has the potential to result in substantial performance improvements for 64-bit capable guest operating systems that are currently constrained by the 2G limit. The support provided in z/VM 3.1.0 for real storage sizes larger than 2 Gigabytes means that the same applies to z/VM itself when run second level or on actual hardware.

Section Real Storage Sizes above 2G provides some examples of z/VM running CMS workloads in real storage sizes larger than 2G. However, for those examples, z/VM also runs these same workloads quite well in a combination of 2G real storage plus the remainder of total storage configured as expanded storage. Because performance is good to start with, these examples show only incremental performance improvements when additional real storage is substituted for expanded storage.

VCTC Pathlength Reduction

The pathlength in CP that implements virtual channel-to-channel has been reduced significantly by improving the efficiency with which the data are copied from source to target virtual machine. Measurement results (see Virtual Channel-to-Channel Performance) show a 53% reduction in CP CPU time and a 64% increase in throughput. This improvement was first made available in VM/ESA 2.4.0 through APAR VM62480 and has now been incorporated into z/VM 3.1.0.

Miscellaneous CMS Improvements

A performance improvement has been made to the Rexx compiler's runtime library and this improvement has been incorporated into the version of that library that is integrated into CMS for use by CMS functions that are implemented as compiled Rexx programs. This improvement decreases the number of Diagnose 0 requests that the runtime issues in order to determine the level of CP that it is running on. The net result is a decrease in CP CPU time when using the CMS productivity aids (FILELIST, RDRLIST, PEEK, etc.) and other CMS functions that are implemented in compiled Rexx. This improvement reduces total system processor requirements of the CMS1 workload by about 0.2%.

There has been further use of the SUPERSET command to replace multiple instances of the SET command in XEDIT parts used in the CMS productivity aids. This has resulted in reduced processing requirements for CSLLIST, NAMES, CSLMAP, MACLIST, and VMLINK.

Gigabit Ethernet Support via QDIO

The QDIO support in TCP/IP Level 3A0 allows for the support of Gigabit Ethernet connections with a high level of throughput capacity. See Queued Direct I/O Support for additional discussion and measurement results.

Contents | Previous | Next