INT 21 - European MSDOS 4.0 - "SETPRI" - GET/SET PROCESS PRIORITY
AX = 8E00h
BH = 00h
BL = action
00h set priority for command subtree
01h set priority for specified process only
CX = Process ID
DH = 00h
DL = change in priority (00h to get priority)
Return: CF clear if successful
DL = process priority
DH destroyed
CF set on error
AX = error code (01h,no such process)(see AH=59h)
Desc:   specify or determine the execution priority of the specified process
or the process and all of its children

See also: 2181

218E00 - European MSDOS 4.0 - "SETPRI" - GET/SET PROCESS PRIORITY