Modifying the z/VM guest LAN type

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To study the impact of the z/VM® guest LAN type, we ran several tests interchanging HiperSockets™ and QDIO and varying the MFS size parameter.

See z/VM Guest LAN type setup for details on our setup for these tests.

Because the WebSphere® Load Balancer does not support a HiperSockets connected network, we bypassed the WebSphere Load Balancer for these measurements.

Figure 1 shows the impact of switching the z/VM guest LAN type from QDIO to HiperSockets and varying the MFS size parameter.

tnwasext6 — Figure 1. Varying network types and MFS size

Observations

Switching the guest LAN type to HiperSockets increased the throughput by 4%, which is further improved when enlarging the MFS size to 24 KB. The final increase, compared to QDIO is 7%. It is also interesting that the response time is reduced by 3 ms. One explanation is that software emulation of guest LAN type HiperSockets has a shorter path length than guest LAN type QDIO.

Conclusions

Generally, from a performance view point, the usage of the guest LAN type HiperSockets instead of QDIO could be recommended for this type of workload. Unfortunately, the missing support for the WebSphere Load Balancer forces the use of QDIO if the WebSphere Load Balancer is required.