Introduction

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General information is provided in this topic about the z/VM® 6.3 HiperDispatch feature and the testing results described in this White Paper.

The HiperDispatch feature and APAR VM65586

z/VM 6.3 introduced the HiperDispatch feature that takes CPU topology into account when scheduling virtual CPUs. Our testing processes produced unexpectedly high values for the percentage of state samples that showed a virtual CPU to be waiting for a logical CPU, reported in the z/VM Performance Toolkit report USTAT.

By applying the z/VM 6.3 z13 SPE (APAR VM65586 and related) we did achieve a noticeable performance improvement. However, it did not improve the observed behaviour. We found that the CPU dispatch polarization mode a had significant influence on dispatch delay times and CPU usage.

This paper analyzes the performance impact of both the above items when applied to a typical customer mixed-workload running on an IBM zEnterprise 196.

Notational conventions

Table 1 shows the notation conventions used in this paper, in accordance to IEC 60027-2 Amendment 2.

Table 1. Notation conventions
Table with three columns that contain information about notation conventions used in this paper.
Symbol	Full name	Derivation
KiB	kibibyte	2 ** 10 byte == 1024 byte
MiB	mebibyte	2 ** 20 byte == 1048576 byte
GiB	gibibyte	2 ** 30 byte == 1073741824 byte