Hi,
 
I have done a nodebug kernel [1] on soas;KDE;LXDE with 32 GB microSD cards. All work smoothly and much faster afterwards.

That's to be expected, rawhide always has debug turned on except for the first build of each RC.

Once we branch the debug gets turned off.
 
"sd-host-bcm2835-not registering properly" so debug kernel keeps trying to register it until it fills up the card.

I don't know what you mean by this, can you provide details an the kernel version?
 
Is there a missing file on the f31 spin .  .raw files that precludes registration?


I notice that the arm file:

   ubuntu-mate-18.04.2-beta1-desktop-armhf+raspi-ext4.img    Has a "sd-host-bcm already registered - abort " on boot

Again, I need context here, I've never used Ubuntu on Arm, let alone a Raspberry Pi, what kernel version?
 

This debug messaging appears to dominate all 3 spins to the point that only a very few processor cycles are devoted to the spin itself.

Well I'm not surprised by that, it's the same kernel.
 
This almost requires using a nodebug kernel to test spins on the Rpi3B+

So wait until we branch, or wait until Tuesday when we have a compose that contains the 5.3-rc1.0.1git kernel which will have debug turned off. The general rule of thumb is that the Tuesday compose, if successful, will have the nodebug kernel in it and the change isn't so great that if you test each Tuesday's release that you'll be fine.

Peter

PS please always send mails like this to the list so others can answer/see answers.