ID 328159 - ZDefocus has less CPU utilisation when using more threads

Problem summary
ZDefocus has less CPU utilisation when using more threads.

On Linux, the more threads you have, the less CPU utilisation there is, 8 threads averaged around 80% whereas 48 threads had 30%.
On Mac, the more threads you have, the less CPU utilisation there is, however this affects the ZDefocus and Defocus in the same way, whereas it only affects the ZDefocus node on other operating systems.
On Windows, the CPU utilisation is always 70%-80%, so does not appear to be affected in the same way.
Customer reported version
nuke.11.0v3

Customer reported platform
centos6

Steps to reproduce

1) Open Nuke and open the attached Nuke script

2) Open System Monitor and view the CPU utilisation

3) View the Defocus node and playback the Nuke viewer

4) Observe the System Monitor, the usage should be 100% when rendering, as shown below:

​

5) View the ZDefocus node and playback the Nuke viewer

6) Observe the System Monitor, the usage will be a lot lower, how much depends on the number of threads you have in your system, as shown below:

​

Workaround
Unknown.

Reproduced by support
This bug has been reproduced in:
Nuke 11.1v1 - CentOS 7.3 - MacOSX 10.13
Nuke 11.0v3 - CentOS 7.3
Nuke 11.0v1 - CentOS 7.3
Nuke 10.5v7 - CentOS 7.3
Nuke 10.5v1 - CentOS 7.3
Nuke 10.0v6 - CentOS 7.3
Nuke 10.0v1 - CentOS 7.3
Nuke 9.0v9 - CentOS 7.3
Nuke 9.0v1 - CentOS 7.3
Nuke 8.0v7 - CentOS 7.3
Nuke 8.0v1 - CentOS 7.3
Nuke 7.0v10 - CentOS 7.3 - MacOSX 10.13

Unable to reproduce bug in:
Nuke 11.1v1 - Windows 10
Nuke 11.0v3 - Windows 10
Nuke 7.0v10 - Windows 10

Earliest version tested
Nuke 7.0v10 - This issue appears to be in all versions of the product

Expected behaviour
For the ZDefocus node to have the same CPU usage as the Defocus node

Actual behaviour
On Linux, the more threads you have, the less CPU utilisation there is, 8 threads averaged around 80% whereas 48 threads had 30%.
On Mac, the more threads you have, the less CPU utilisation there is, however this affects the ZDefocus and Defocus in the same way, whereas it only affects the ZDefocus node on other operating systems.