Quick dispatch (QUICKDSP)

The purpose of these tests was to see the impact of the quick dispatch option. When the quick dispatch option is assigned to a virtual machine, that virtual machine is added to the dispatch list immediately, whenever it has work to do, without waiting in the eligible list. We assigned it to all guests.

Observations

Looking at Figure 1 and Figure 2 we see that using the QUICKDSP option with Linux® z/VM guests provided a significant benefit when the resources are overcommitted, like CPU and memory for five triplets and there is a resource constraint. Otherwise, there was no benefit to using QUICKDSP.

The CPU costs also remained nearly the same, regardless of whether there was CPU overcommitment.

Conclusions

Using QUICKDSP for the z/VM guests can bring a benefit when the resources (CPU, memory) are overcommitted and resources are constrained.