1 03/25/74  Load Control Groups
 2 
 3 Load control groups control who gets logged in.
 4 Each project is assigned to a load control group, which has
 5 a quota of guaranteed primary load units.
 6 When a user logs in, he is assigned "primary" status
 7 if his load control group is not full. He gets a message
 8 of the form
 9      You are protected from preemption until 1832.
10 which tells him how long he may keep primary status.
11 
12 If a user's group is full, but the system is not full,
13 he may be assigned "secondary" status and receive the message
14 
15      You are subject to preemption.
16 
17 This warns him that a primary user may preempt (bump) him
18 in order to log in, if the system is full.
19 
20 Users who are preempted are given a three-minute warning
21 before automatic logout, which looks like this:
22 
23      **********
24      From Multics: Secondary user preemption.
25      You will be logged out in 3 minutes.
26      **********
27 
28 
29 Login decision:
30 I. System is not full
31    A. Group is not full --> login as primary
32    B. Group is full, search primary users of same group
33       1. Found primary user with expired grace --> demote him
34           to secondary and login as primary
35       2. No user with expired grace --> login as secondary
36 
37 II. System is full
38    A. Group is not full --> must be a secondary on system,
39        preempt him and login as primary
40    B. Group is full, search primary users of same group
41       1. Found primary user with expired grace --> preempt him
42          and login as primary
43       2. No user with expired grace --> sorry, system full. no login.
44 
45 For preemption or demotion, the user who logged in first is the
46 first candidate.
47 
48 Secondary users are promoted to primary if a primary user
49 from the same group logs out. Here too, the user who logged in first
50 is the one who is promoted.