HP OpenVMS Systems

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Scheduling: Realtime priority

The Question is:

I had a interactive process set at priority 63.  All our
SCADA processes have process priorities between 17-29.
One of the processes running at 29 went in a tight loop.
I could not recover from the loop even though
I had a interactive process running at 63.
I changed to 31, still didn't help we had to crash the
system.  Have never seen this on VAX platforms
before. ( Our programs have gone in a loop on VAXes too !)

Any suggestion would be appreciated.

The Answer is:

On a DECwindows workstation, the DECW$SERVER_0 process and DECW$TE_xxxx need to
get some amount of compute time to service the keyboard/mouse input and display.

By boosting the relevant process priorities to 31, I was able to monitor/control
a looping process at 30.

    Since you don't say how the priority was set, you need to beware that
    in internal representation priorities are backward, so if you changed
    the priority from K-mode code and wrote the priority with 63, it actually
    would mean priority 0.