For the official competition harness, see the VU demo contest project at this site -> https://playstation2-linux.com/projects/vudemocontest.
This harness is a spin off from that which should work the same way, but there are no guarantees.
First of all, Sauce made some improvements to the harness which added 2 controls whilst a demo is running:
Hold down SELECT and press L1 to dump the contents of VU mem to a file - perfect for use with my GIFtag disassembler (soon to get it's own project)
Hold down SELECT and press START to reload all demos - handy if you've just compiled a new version of the one you're working on.
Then, I added a performance bar that shows you how busy the VU is per frame. You should see a green bar starting at the top of the screen, and working it's way down the side.
That bar is measures how busy the VU is. If the screen is mostly black, then the VU is sitting still, happily waiting for the screen to update every frame. If it's mostly green, then the VU is working hard to keep up.
If the VU works so hard that it can't complete execution in a single frame then you'll start to see flashing green/black - this is bad!
Note: I've had reports that some TV or monitor setups don't allow enough room for you to see a coloured border around the screen - if this is the case try fiddling with your monitor controls until you see something.
The SPS2 project has some sample code which sets the background colour - if you can't see that then you can't see the performance bar either.