1 Assume that two virtual .achines are to be added to the eligible
list for Q2. The paging bias factor is 1, the user bias factor is
1, and the priority delay factor is o. Virtual .achine A has a
projected working set size of 80 percent of available storage and a
user priority of 50. Virtual .achine B has a projected working set
size of 20 percent of available storage and also has a user
priority of 50. The biases are obtained as follows: Paging Bias 80 1-'1 20 1 1 User Bias
+ 501'1 .. 50 1 1 Weighted Bias
= 130/2 = 65
= 70/2 = 35
If 1 is added to the eligible list at base time 0, its eligible
list priority is 65. If the priority delay factor is 0, B is added of A provided that B is eligible for entry to the list within
the next (65-35) 30 seconds. If the priority delay factor is set
to +1, the base is incremented once every two seconds. Therefore,
although the bias difference is still 30, the delay time is now 60 seconds. To force A to be given a weighted bias equal to B, a priority
differential is calculated as follows: 80 + A 20 + B
------ = ------
2 2 A = B - 60 Therefore, for the biases to be equal, A .ust have a priority of 60 less than B. For exa.ple, if 1 is given a priority of 10 and B is
given a priority of 70, the biases would coapute as follows: J Paging _Bias_ 80 1 1 f- 20 1 1 + User -1!i§L 10 1 1 70 1 1 Weighted Bias
= 90/2 ;;-45-- = 90/2 = 45 The large difference in priorities could be lessened by increasing
the user bias If the user bias factor is set to 3 instead
of 1, the calculated priority differential is as follows: 80 + 3A 20 + 3B -------= 4 4 3 (B -A) = 60 1 = B - 20 lOw, 1 requires a priority of only 20 less than B to achieve
parity. For exaaple: 1-130 IBM VM/370 Systea Logic and Problem Deteraination--Voluae 1

Paging User Bias Bias 8oX'1 ... 30X3 == 20 X 1 + 50 X 3 =
Weighted
Bias 170/4 = 42 170/4 = 42
The above examples illustrate the following general points about the use
of the bias factors, the delay factor, and the user priority value:
1. The paging and user bias factors are a measure of the relative importance of the bias value. A high user bias allows greater
discrimination via the assigned priority; while a high paging bias makes storage requireaent the primary scheduling parameter. 2. The virtual machine priority
overridden, and is the means
improved perforaance.
value, in the directory, aay be
through which selected users obtain
3. The priority delay factor is the aeasure of the impact that the
paging and user biases are to have. The greater the delay value,
the greater is the maximum delay that can be experienced by a given
user.
4. The interactive bias factor is a tool that enhances coaaand
response to conversational commands that require disk I/O, and that may be partially executed in Q2.
If the paging ·bias factor is nonzero, the net effect of the priority scheme is to discriminate against virtual machines that require large
aaounts of real storage. This discrimination results in a higher leyel of multiprogramming and increased processor utilization; however, it must be traded off against poorer throughput for large storage users.
The distributed scheduler is not biased; the bias factors are as
follows: --- Paging bias factor (DMKSCHPB) = 0 User bias factor (DMKSCHUB) = 1
Priority delay factor (DMKSCHPD) = 0 Interactive bias factor (DKKSCHIB) = 0 Thus, the basic YM/370 scheduler schedules virtual machines FIFO within
user priority.
Figure 19 is a graphic breakdown of the user states, showing the
relationship between interactive and non-interactive states, in-queue
and not-in-queue states, and in-list and not-in-list states. , i 1 In-Queue 1 Bot-in-Queue 1 1------------------------------ I IDispatch I Bo IEligible I Bo 1 1 List IListl List IListl r I 1 In teracti ve 1 1 2 3 4 I 1------------------------------------------ I I Non-Inter- I I 1 active I 5 6 7 8 1 Figure 19. User Dispatching States CP Introduction 1-131