> In my case I don't want it to ever interrupt the higher-priority "system" processes (event tickler, low space watcher, finalizer), but the "last" user process. Not quite sure how to determine that, though.
>
> Crazy idea: On user interrupt, sample the system for 100 ms to see which process takes up so much time. Too crazy? ;)

But, IIUC, wouldn't such a sample would probably lead to the same
answer (e.g., the finalization process), if that is the process that
is consuming a lot at that moment..?

I don't quite remember the status of Igor's finalization enhancement
in the image and VM - a simple pointer swap was able to take the place
of full-enumeration of the finalization list.  My gut tells me the
support is in the Cog VM but that there might be some concurrent
access issues on the image side..