Suggest the non-symlink path to the interpreter for core.rush() on Debian-derived systems

[aforren1]

Really minor thing, setcap only operates on non-symlink files. It looks like Python 3 has been the default python since Ubuntu 20.04, so also updated that text to reflect the likely system Python.

[peircej]

I'm actually now not certain how this interacts with the suggested config setting at https://github.com/psychopy/psychopy/blob/dev/psychopy/app/linuxconfig/__init__.py#L39
My memory is that allows anybody in the psychopy group (to which the user is added) to re-nice to -20 without needing sudo (but I think that's not taking effect unless you then call rush)

[aforren1]

Thinking about it more, I think the config should be the way to go rather than setting the capabilities on the executable (i.e. replacing the setcap recommendation).

However, a member of the psychopy group might not be able to set the priority currently requested in rush (50 < sched_get_priority_max()). Either the sched_priority needs to be reduced to fall within the upper bound set by rtprio in the config, or the config needs to bump the allowed rtprio up to the 99 (see the sched_setscheduler man page). Maybe the former? FWIW, PTB recommends using the minimum realtime priority.

[peircej]

Right, yes, I agree. We certainly want 99-psychopylimits.conf to be compatible with the actual call to rush, and If PTB now recommends a lower value to achieve good timing while still playing nice that sounds ideal to me (and means the code can change without changing the existing config files)