MCS-378 Lab 1: Scheduling Experiments, Fall 2001

Due: September 24, 2001

In this lab, your group will experiment with programs that load the linux system up with processor and/or filesystem activity. Be sure that you kill these processes off before logging out, as you will otherwise be quite unpopular with whoever uses the machine next, since these processes are designed precisely to be resource hogs. If you are running one of these programs in the foreground in an xterm window (as I suggest), you can just use control-C to kill it. Otherwise you can use the kill command. The reason to run the programs in the foreground, each in their own xterm window, is that they print periodic reports of how long it took to do the last batch of iterations.

The two programs you will use are runner.c and writer.c; each is linked into the web version of this assignment. One does lots of running and the other does lots of writing to a file. To compile them you would use the commands

cc -o runner runner.c
cc -o writer writer.c

To run the runner (for example) you would use

./runner

There is almost zero programming to do in this lab and the experimental procedure is relatively simple and is spelled out for you, so the key is going to be for your group to write a good lab report that reports what you observed and provides some interpretation of those observations.

Run one, two, three, and four copies of runner and observe how long they report they are taking (as a function of how many there are). Also, in yet another xterm window, run the top program and see what percentage of the CPU each runner process is getting (again, as a function of how many there are).
Run two copies of runner and have a partner log into the same machine and run one additional copy of runner. (Thus you will have three copies running, two under one user and one under another.) Again, observe their reported times and top's report of their CPU percentages. Is linux's scheduler giving a fair share of the CPU to each user or to each process?
Run one copy of writer and observe its reported times, top's report of its CPU percentage, and vmstat's report of the blocks written out. (To run vmstat, in another xterm window give the command
```
vmstat 10
```
The first line of statistics is since the machine was booted, and isn't useful. However, thereafter a new line will be output every 10 seconds (since you specified 10) reporting on activity in the preceding 10 seconds. The column headed "bo" is the one showing blocks written out.) Is the writer doing lots of actual writing to disk? (You can also look at the machine's disk light and listen for disk sounds.)
Follow up on the preceding question by reading the man page for the fsync system call, which ensures data written to a file descriptor is actually written to disk. (An alternative to the man page would be to look it up in Stevens's book, which we have in the monitor room.) Insert an appropriate call to fsync in the inner loop body of writer.c so that it is forced to go to disk every time it writes a character. Redo the observations from the preceding question. You may need to reduce the number of iterations that are timed. Are the results quite different?
Run one runner concurrently with one modified writer and observe their performance reports and the statistics from top and vmstat. How does each program's performance when they are run together compare with that when run alone?

Instructor: Max Hailperin