CS457 - System Performance Evaluation - Winter 2010

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Mid-term conflicts
Assignment 1. There are three general problems in this assignment:
- Many of the students did not separate the parameters and factors. When they listed the parameters, they actually meant the factors.
- Most of the students noted that the bandwidth is something important, but they still put it in the system parameters in part 2. They did not understand the change from part 1 to part 2.
- Some students just copied the example in class, and provided many items about the internal stuff. We cannot say it's wrong, but I do not think they understand the lecture very well.
Assignment 1 office hours
- 15.00 to 17.00 Friday (today)
- 15.00 to 17.00 Monday
- DC3549.
Assignment 2.

Design for analysis

Games like Halo or The Sims
- Halo: simulate physics and biology using simplified models of physics and biology that provide adequate look, sound and feel.
- The Sims: simulate human cognition & feeling, and also inter-human interactions
Pre-fabrication testing of computer hardware
- Simulate instruction execution using a slow speed implementation on an existing CPU.
- May include
  - instruction timing (for threading)
  - heat generation
  - electron density over time
  - etc.
- Uses simplified workloads
- Normally follows on from a more primitive form of simulation, usually called hand execution.
Wizard of Oz methods in User Interface design
- Simulates interface operation by having a human that plays the part of the computer.
- More interestingly (in the sense of "May you live in interesting times.") done by Flash et al.

These models have in common the need to simplify either

Based on a model, which is an abstraction of the system.

**Common Model Contrasts**
	Continuous	Discrete
Determinism	Fully deterministic	Details modelled probabilistically
State	Continuous e.g. know that processing is x% complete	Discrete: change system state only when things start of end (events)
Time	Make time steps as small as possible.	Time moves forward discontinuously, from event to event

You did this before
- Understand the system
- What is the goal?
- Determine the components
  - e.g., server, job
  - sometimes called `entities'
  - have attributes, e.g.
    - server: capacity
    - job: service required
    - system (client?): interarrival time
- Cheat and steal
  - There must be some reason for lying as well.
Select the type of queueing model
- single server queue,
- single service facility with multiple servers,
- network of queues
Specify attributes that need algorithms
- e.g., scheduling disciplines for resources
Specify workload parameters and performance metrics
- remember (guess what?) the goal

single server, two classes of request (maybe two different products being supported)
queueing models have a scheduling algorithm, such as
1. FCFS
2. priority-based FCFS
3. round robin, aka take turns
each has a natural structure
1. FCFS: single queue
2. priority-based: multiple queues
3. round-robin: multiple queues
with multiple classes
- arrival rate adds: r = r1 + r2
- interarrival time adds reciprocals: t = 1/r = 1/(r1 + r2 ) = 1/(1/t1 + 1/t2) = t1*t2 / (t1 + t2)
  or 1/t = 1/t1 + 1/t2
Parameters
- interarrival time: per class
- length of transaction: per class
- service capacity: per class
- queueing algorithm
Performance metrics
- waiting time: per class
  This is used to determine the cycle time of the advertising you listen to. Just joking!
- utilization
  No point in hiring any more support staff than you need.

For a more CS-like example see this pdf.

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