rdisp/prio/upd is a SAP Parameter attribute which is used to control Priority class of UPD work process information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
Introduction of four relative priority classes based on the priority defined in the job description (JOBD):
HH (JOBD - 10) H (JOBD - 5) M (JOBD) L (JOBD + 5) MS, DISP, ENQ, GW : HH UPD : H, M rdisp/prio/upd DIA, UP2 : M BTC : M, L rdisp/prio/btc SPO : M, L rdisp/prio/spo
The priority in the JOBD must be between 15 and 80, if not, a warning is put out and JOBD is set to 20 (for JOBD <(><<)> 15) and to 80 for JOBD <(>><)> 80.
Priority adjustment is only possible if the dynamic priority scheduler in OS/400 is switched on (system value QDYNPTYSCD = 1).
The user is then allowed to specify the priority classes for UPD, BTC and SPO. Every other process has a fixed relative priority.
If QDYNPTYSCD = 0 and the parameters have values other than M, a warning is put out and all processes are running at JOBD.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.