gparmer / fork-onacci

Have fun with fork!

Fork-onacci

Having fun with fork! Or at least burning some cycles.

Today, we're going back to 1112, and mastering recursion. Remember good 'ol fibonacci:

fib(0) = 0
fib(1) = 1
fib(n) = fib(n - 1) + fib(n - 2)

If it is good enough for the golden ratio, it's good enough for a class exercise!

Task 1

Implement fib in C. I know, real hard.

Task 2

Use fork, exit, and wait to calculate fib...fibork! Each recursive "call" to fibork should be in a new process. You should not use fib in your implementation, and each call to fibork should result in creating two children processes, each of which call fibork for the recursive call. You'll have to think about how fork works to figure out how to pass the argument. To "return", you'll need to exit, and to pass the return value, the exit value will need to percolate to wait. Note that when wait(&status) gets the status from exit, you must use WEXITSTATUS(status) to access its value.

You can use man to figure out how to use these calls appropriately.

Task 3

Change the optimization settings from -O0 to -O3, and recompile (make sure to run make clean). Form a hypothesis:

• What will happen to the performance of each implementation?
• How much will they improve?

Then execute the system. Does it match your hypothesis? Why or why not?

Task 4

Remember our old friend, objdump? Lets figure out why the performance changed? Use objdump -S and look at your function's implementation. If you want to more easily search through objdump's output, you might consider outputting to a file (e.g., objdump -S bin > output.txt). What made it faster?