Comment 25 for bug 1838575

I could next build a test kernel with some debug around the vfio iommu dma map to check how time below that call is spent.
I'm sure that data already is hidden in some of my trace data, but to eventually change/experiment I need to build one anyway.

I expect anyway to summarize and go into a discussion at some point, as even if one would split the map calls iommus are full of quirks and constraints that might bit us later.