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Summary of Key Findings

This section summarizes the performance evaluation of z/VM 4.3.0. For further information on any given topic, refer to the page indicated in parentheses.

Performance Changes 

z/VM 4.3.0 includes a number of performance enhancements, performance considerations, and changes that affect VM performance management (see Changes That Affect Performance):

  • Performance Improvements
    • Enhanced Timer Management
    • Improved Utilization of Large Real Storage
    • Improved Linux Guest QDIO Performance
    • TCP/IP Stack Improvements

  • Performance Considerations
    • Guest FCP I/O Performance Data

  • Performance Management Changes
    • Monitor Enhancements
    • CP I/O Priority Queueing
    • Virtual Machine Resource Manager
    • Effects on Accounting Data
    • VM Performance Products

Migration from z/VM 4.2.0 

Regression measurements for the CMS environment (CMS1 workload) and the VSE guest environment (DYNAPACE workload) indicate that the performance of z/VM 4.3.0 is equivalent to z/VM 4.2.0.

CPU usage of the TCP/IP VM stack virtual machine has been reduced significantly, especially when it serves as a router. For that case, CPU time reductions ranging from 24% to 66% have been observed (see TCP/IP Stack Performance Improvements).

New Functions 

The CP Timer Management Facility now uses the scheduler lock for multiprocessor serialization instead of the master processor. This change reduces master processor constraints, particularly on systems that produce large volumes of CP timer requests. This can be the case, for example, when there are large numbers of Linux guests (see Enhanced Timer Management).

VM Guest LAN was introduced in z/VM 4.2.0 and simulated the HiperSockets connectivity. With z/VM 4.3.0, VM Guest LAN has been extended to also simulate QDIO. Measurement results indicate that this support offers performance that is similar to previously available connectivities (real QDIO (Gigabit Ethernet), VM Guest LAN HiperSockets simulation, and HiperSockets) (see VM Guest LAN: QDIO Simulation).

z/VM supports the IBM PCICA (PCI Cryptographic Accelerator) and the IBM PCICC (PCI Cryptographic Coprocessor) for Linux guest virtual machines. This support, first provided on z/VM 4.2.0 with APAR VM62905, has been integrated into z/VM 4.3.0. The measured SSL environment showed a 7.5-fold throughput improvement relative to using software encryption/decryption (see Linux Guest Crypto Support).

CP storage management has been modified to more effectively use real storage above the 2G line in environments where there is little or no expanded storage. Measurement results for an example applicable environment show a substantial throughput improvement (see Improved Utilization of Large Real Storage).

With z/VM 4.3.0, you can now collect accounting data that quantifies bytes transferred to/from each virtual machine across virtualized network devices (VM guest LAN, virtual CTC, IUCV, and APPC). Measurement results indicate that the collection of this accounting data does not appreciably affect performance (see Accounting for Virtualized Network Devices).

CMS minidisk commit processing has been improved. The number of DASD I/Os done by CMS minidisk commit processing for very large minidisks has been reduced by up to 95%. This improvement has little or no effect on the performance of minidisks having less than 1000 cylinders (see Large Volume CMS Minidisks).

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