Feature: Properly warn if no realtime kernel is active

[hdiethelm]

If you don't have a real time kernel running, you only get a small note in the console: Note: Using POSIX non-realtime

If you start only the gui and use a standard config, you don't see it at all.

This can easily happen anytime:

• If you have multiple kernels installed and pin it by GRUB. If you install a new kernel, the order can change and the wrong one starts.
• You forget setsuid / setcap in source builds

It might be beneficial to show an error in the gui that can be disabled by config if you don't want to use a real time kernel.

[hdiethelm]

For my config, I just added a permanent jitter display in axis.

If all is good:

If it looks like this, something is wrong:

[BsAtHome]

It might be beneficial to show an error in the gui that can be disabled by config if you don't want to use a real time kernel.

Well, that is (very) annoying in development, unless it is somewhere in the GUI that does not change the current layout. Error popups are out of the question IMO. You need a (clearly) visible yet non-intrusive way to do this.

[hdiethelm]

Just an idea that could improve general perceived stability.

I don't suppose to show always the jitter value, this is just how I do it on my setup. This never happened to me for now but I see it coming... ;-) That's why I added the jitter display.

For example, there are this red popup's that are coming from emcmot errors. Might be there is a way to trigger one like this somehow. And disable it by an environment variable / ini value if someone really want's to use linuxcnc without real time.

There is already the real time overrun error. But it is disabled when you don't have an RT kernel:

linuxcnc/src/rtapi/uspace_posix.cc

Line 168 in 3cd702c

if (policy == SCHED_FIFO)