I am developing a server-side application using Java and OSX and quite often I have to run a rather large test suite to make sure everything is alright. I am using IntelliJ IDEA (Java-based IDE).
When I use one workspace only, tests finish in about ~3 minutes no matter whether the IDE has focus or not. It just has to be in the same workspace.
When I move the IDE to a different workspace (so I'd have 2 workspaces) or into fullscreen mode (which essentially creates a new workspace), test execution is ~100% slower (takes about 6 minutes).
When I keep the focus in the second workspace for the whole execution time period, we're back to ~3 minutes.
This is really puzzling to me. I measured it using various number of workspaces and various number of applications per workspace, same results.
Clarification from the discussion from the comments, to avoid confusion:
If the focus in in the workspace with the IDE or full-screen IDE, it's fast. Once the focus is on a different workspace (so the IDE is either on a different workspace or in a full-screen mode (but with no focus)) then it is slower.