CS411/511. Operating Systems

## Maillist Archive, Spring 1999

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Re: Homework question 5.7 makes no sense.

```this does not say that A and B are positive.  A and B are rates of change.
In (a), both cause a process's priority to increase from zero.  In (b)
they both cause a process's priority to decrease from zero.  (Note that
all start at zero.)

=============================  yournote  ============================

5.7   Consider the following preemptive priority-scheduling algorithm based
on dynamically changing priorities.  Larger priority numbers imply6 higher
priority.  When a process is waiting for the CPU (in the ready queue, but
not running), its priority changes at rate A; when it is running, its
priority changes at rate B.  All processes are given a priority of 0 when
they enter the ready queue.  The parameters A and B can be set to give many
different scheduling algorithms.

a.  What is the algorithm that results from B > A > 0?

b.  What is the algorithm that results from A < B < 0?

The first thing that strikes me as strange is that A and B are both
positive.  Normally, in this type of system, A is positive and B is
negative.  The priority for a process is normally >= 0.  I ran through
these processes setting B=2 and A=1 (for a.) and this is the order I saw
for three processes one unit apart: 11122112331221... What algorithm does
this fit?

Question b. came out as LIFO.

I am confused.

Roy
```

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