I know rt-sources are not supported by Gentoo in any way, so I'll accept a "no thanks" in good cheer. But this is a note about Nouveau, not rt-sources. When I use the in-kernel Nouveau drivers, I get a steady stream of xruns from JACK, about two per second. I have confirmed another user I support with the same issue. The issue disappears (few to no xruns) when we stop using the Nouveau driver and switch to nvidia-drivers.
Steps to reproduce:
1. Have an Nvidia card
2. emerge rt-sources
3. genkernel all
4. Run JACK (qjackctl or Cadence)
5. Note xruns
Switching to nv results in fewer xruns, however, the number of xruns is still unacceptable in this case, and is clearly tied to graphic events on-screen.
This issue does not exist when the video card is something other than Nvidia.