macOS app nap: effecting performance of VirtualBox VM

[PikeSandwich]

host macOS 10.14.5 (Mojave) iMac 19,1 (Intel i5, 6 core, 40GB RAM), guests linux (ubuntu 19.04, Windows10 1809) the VirtualBox VM process will get AppNap'd by macOS resulting in:

1. approximately 20-25% performance compared to when AppNap=no for cpu-bound guest process
2. while degraded, host still reports full CPU core consumption. to be clear, if running 1 cpu-bound guest process, when AppNap=no host reports 100% CPU utilitizatiion (expected), when AppNap=yes host still reports 100% CPU utilization (not expected).
3. this does NOT happen when VM is run headless (presumably because AppNap targets .app with GUI contexts)

Steps taken to produce problem:

1. rm VBox.log
2. launch linux guest with head
3. ssh into linux guest
4. launch spin.rb script to loop/bump counter, and every 1.0 second emit count/reset-count, output is @4,400,000/s
5. minimize (yellow button on macOS host) guest head
6. watch Activity Monitor.app CPU tab with added field App Nap and filter on virtualbox, and notice VirtualBox VM nap=no
7. watch Intel Power Gadget.app Frequency monitor, core pegged at turbo rate of 4.0GHz
8. wait for something around 30-60 seconds passes
9. notice (3) changed output from @4,400,000/s → @1,200,000/s
10. notice (5) changed nap from no → yes
11. notice (6) changed from 4.0GHz → 2.0GHz and stabilized at 1.5GHz
12. wait an arbitrary 45 seconds or so
13. un-minimize previously minimized guest head (from step (4))
14. notice (3),(5),(6) change back to output @4,400,000/s, nap=no, core=4.0GHz
15. shutdown linux guest
16. save VBox.log

related forum thread:  https://forums.virtualbox.org/viewtopic.php?f=8&t=93183

[PikeSandwich]

ruby script to spin cpu report iterations per second

[PikeSandwich]

log showing drop in spin.rb running in linux ubuntu 19.04 guest

[PikeSandwich]

activity monitor filtered to virtualbox, and sorted by appnap column

[PikeSandwich]

Intel Power Gadget core frequency monitor drop coninciding with appnap=yes

[socratis]

Related discussion in the forums:  https://forums.virtualbox.org/viewtopic.php?f=8&t=93183

It's worth mentioning that this issue was discovered independently from a user in the Apple forums:  https://discussions.apple.com/thread/250276999