Summary of Key Findings
This section summarizes key z/VM 6.4 performance items and contains links that take the reader to more detailed information about each one.
Further, the Performance Improvements article gives information about other performance enhancements in z/VM 6.4.
To compare the performance of z/VM 6.4 to the performance of previous releases, IBM ran a variety of workloads on the two systems. For the base case, IBM used z/VM 6.3 plus all Control Program (CP) PTFs available as of March 31, 2016. For the comparison case, IBM used z/VM 6.4 at the "code freeze" level of August 15, 2016. The runs were done on a mix of zEC12 and z13.
Regression measurements comparing these two z/VM levels showed improvement on z/VM 6.4 compared to z/VM 6.3. ETRR had mean 1.10 and standard deviation 0.25. ITRR had mean 1.15 and standard deviation 0.37.
Runs showing large improvements tended to be either memory-constrained workloads that got the benefit of the memory management and paging work or networking runs that got the benefit of repairs to the handling of jumbo frames. Most of the rest of the runs showed ratios in the neighborhood of 1.
Key Performance Improvements
z/VM 6.4 contains the following enhancements that offer performance improvements compared to previous z/VM releases:
Memory Constraint Relief and 2 TB Exploitation: z/VM can now use a central storage size of 2 TB (2048 GB). This is due in part to serialization constraint relief that was done in the memory management subsystem. For more information, read the chapter.
Other Functional Enhancements
These additional functional enhancements since z/VM for z13 are also notable:
CP Scheduler Improvements: In 2014 a customer reported z/VM's scheduler did not observe or enforce share setting correctly in certain situations. z/VM 6.4 made repairs to the scheduler. For more information, read the chapter.
Encryption of RSCS TCPNJE Connections: In z/VM 6.3 with the PTF for APAR VM65788 IBM shipped service for RSCS that will let it encrypt the traffic that flows across a TCPNJE link. To accomplish this RSCS exploits z/VM TCP/IP's Secure Sockets Layer or SSL. Though there is some performance impact compared to running the TCPNJE link unencrypted, some customers might wish to make the tradeoff. For more information, read the chapter.
TCP/IP Encryption Uplift: In z/VM 6.4 certain TCP/IP encryption defaults are strengthened and a new version of System SSL is present. Using two Telnet workloads IBM evaluated all of these changes. For more information, read the chapter.