THE ABSTRACTION: THE PROCESS

$12$

Homework $($Simulation$)$

This program, process$-$run. py$,$ allows you to see how process states change as programs run and either use the CPU $($e$.$g$.,$ perform an add instruction$)$ or do I$/$O $($e$.$g$.,$ send a request to a disk and wait for it to complete$).$ See the README for details.

Questions

Run

process$-$run.py with the following flags: $-1,5$:$100,5$:$100.$ What should the CPU utilization be $($e$.$g$.,$ the percent of time the CPU is in use?$)$ Why do you know this? Use the $-c$ and $-p$ flags to see if you were right.

Now run with these flags: $./$process$-$run.py $-1,4$:$100,1$:$0.$ These flags specify one process with $4$ instructions $($all to use the CPU$),$ and one that simply issues an I$/$O and waits for it to be done. How long does it take to complete both processes? Use $-c$ and $-p$ to find out if you were right.

Switch the order of the processes: $-1,1$:$0,4$:$100.$ What happens now? Does switching the order matter? Why? $($As always, use $-c$ and $-p$ to see if you were right$)$

We'll now explore some of the other flags. One important flag is $-S,$ which determines how the system reacts when a process issues an I$/$O$.$ With the flag set to SWITCH$\_$ON$\_$END, the system will NOT switch to another process while one is doing I$/$O$,$ instead waiting until the process is completely finished. What happens when you run the following two processes ${?}^{-}c-S$ SWITCH$\_$ON$\_$END$),$ one doing I$/$O and the other doing CPU work?

Now, run the same processes, but with the switching behavior set to switch to another process whenever one is WAITING for I$/$O $(-11$:$0,4$:$100-c-S$ SWITCH$\_$ON$\_$IO$).$ What happens now? Use $-c$ and $-$p to confirm that you are right.

One other important behavior is what to do when an I$/$O completes. With $-$I IO$\_$RUN$\_$LATER, when an I$/$O completes, the process that issued it is not necessarily run right away; rather, whatever was running at the time keeps running. What happens when you run this combination of processes? $(./$process$-$run.py $-13$:$0,5$:$100,5$:$100,5$:$100-S$ SWITCH$\_$ON$\_$IO $-$c $-$p $-$ I IO$\_$RUN$\_$LATER$)$ Are system resources being effectively utilized?

Now run the same processes, but with $-$I IO$\_$RUN$\_$IMMEDIATE set, which immediately runs the process that issued the I$/$O$.$ How does this behavior differ? Why might running a process that just completed an I$/$O again be a good idea?