CS457 - System Performance Evaluation - Winter 2008

Questions and Comments

  1. Results midterm.

Lecture 20 - More Simulation Examples

Parallel servers: one queue, multiple servers

State variable is number-busy: m

How should it be updated and used?

Finite waiting room

Finite Population Model

Each user does

  1. Think
  2. Wait in queue
  3. Get service
  4. Think
  5. etc.

You might think that there are three event types

  1. Arrive
  2. Start service
  3. Depart

But, "start service" always coincides with either an arrive or a depart event

One thing that is different:

Tandem Queue

You saw this on the mid-term.

The principle is quite easy

but we would rather do this as one simulation. (Programming with signals is not fun.)

The events in the event set are

What happens for each?

  1. A 1.
  2. Dn
  3. DM
  4. start-Sn

Processor Sharing

Time-slicing model: pre-emptive multi-tasking

For example, three classes of jobs

  1. Jobs with active I/O: long think times, very little processing
  2. Interactive jobs without active I/O: substantial processing that will come to an end before long
  3. Batch jobs

Single server, three queues, needs a scheduling algorithm (discipline)

Important state





Broadcast Delivery

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