1. February 12, 2004 Adrienne Noble
Week 6
February 12, 2004
Adrienne Noble

2. Important Dates Due Wednesday, Feb 18 Due Wednesday, Feb 25
Project 3 Experiment Design ( ed to TAs)
Homework 6
Due Wednesday, Feb 25
Project 3

3. Questions?
Midterm
Project 3
Homework 6

4. Project 3 Implement an LRU-like page replacement algorithm
Design and perform an experiment on page replacement algorithms

5. The Scientific Method Four steps
Observe something
Invent a description, or hypothesis
Use the hypothesis to make predictions
Test those predictions with an experiment
Google “scientific method” for more information

6. Running Experiments Control: what is the baseline?
What happens with existing page sizes / page replacement algorithms / no prefetching
New test: what happens with the new system?
Try to change just one aspect of the system to isolate the difference

7. Experiment Ideas
What is the ideal page size for this trace under different amounts of main memory?
How much better is page replacement algorithm X then LRU
“Real” LRU, FIFO, 2Q, ARC, etc
How close can we come to LRU without doing any work between page faults?
No scanning, constant work per page fault
How important is recency vs. frequency in predicting page re-use?

8. Working Set The set of pages that a process currently needs
When is a page in the working set?
When it has been referenced in the last x references
What’s the difference between temporal and spacial locality?

9. Example for (int i=0; i<1000; i++){ int i = 0; int j = 1;
printf(“Hello World”); }
int i = 0;
int j = 1;
int k = 2;
i = j + k;
printf(“Hello World”);
double d = 100;
myFunction(d, j);
printf(“%d”, k);
Temporal locality – locations referenced recently
Spacial locality – locations near locations that have been referenced recently