Question 1:
Run process-run.py with the following flags: -l 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.
Answer:
The runtime should be 100% as the CPU doesn’t waste time on waiting for other process and instead it instantly starts the next one.
Question 2:
Now run with these flags: ./process-run.py -l 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.
Answer:
It takes a total of 11 time. first it ran process 0 4 times at the beginning and then when it was done, it called I/O once then the process was blocked for a total of 5 unit times, and then it ran I/O_end. So calling I/O and ending it took a total of 2 unit times.
Question 3:
Switch the order of the processes: -l 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)
Answer:
So now that the process calls I/O, when it is in the block state it runs the second process while the first process is in the blocked state saving more times running. It took a total of 7 unit times.
Question 4:
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 (-l 1:0,4:100 -c -S SWITCH ON END), one doing I/O and the other doing CPU work?
Answer:
Both should have the same total time because the CPU runs the processes asynchronously.
Question 5:
Now, run the same processes, but with the switching behavior set to switch to another process whenever one is WAITING for I/O (-l 1:0,4:100 -c -S SWITCH ON IO). What happens now? Use -c and -p to confirm that you are right.
Answer:
It behaves as it use to be before changing the flag. My assumption is that it is the default flag.
Question 6:
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 -l 3:0,5:100,5:100,5:100 -S SWITCH ON IO -c -p -I IO RUN LATER) Are system resources being effectively utilized?
Answer:
No, because the first I/O finishes and waits for all other processes to finish until it starts the next I/O.
Question 7:
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 behaviour differ? Why might running a process that just completed an I/O again be a good idea?
Answer:
because running I/O and normal CPU processes simultaneously is the best way to use system resources efficiently.
Faq
Two I/O-related Flags:
-I IO RUN IMMEDIATE: When an I/O completes, the process that initiated the I/O is immediately scheduled to run. The CPU switches back to the process that just finished the I/O.
-I IO RUN LATER: When an I/O completes, the process that initiated the I/O does not run immediately. Instead, the CPU continues running the current process, and the I/O-completing process waits in the ready queue until the OS schedules it later.Two Scheduling-related Flags:
-S SWITCH ON IO: Whenever a process performs an I/O operation, the OS switches to another process immediately (without waiting for the I/O to complete). This keeps the CPU busy by not idling during the I/O operation.
-S SWITCH ON END: The OS doesn’t switch to another process while one is doing I/O; it waits until the process finishes its I/O before continuing with the same process. This could lead to idle CPU time if the process is waiting for I/O.
Question 8:
Now run with some randomly generated processes using flags -s 1 -l 3:50,3:50 or -s 2 -l 3:50,3:50 or -s 3 -l 3:50, 3:50. See if you can predict how the trace will turn out. What happens when you use the flag -I IO RUN IMMEDIATE versus that flag -I IO RUN LATER? What happens when you use the flag -S SWITCH ON IO versus -S SWITCH ON END?
Answer:
-I IO RUN IMMEDIATE:
This ensures faster response for I/O-bound processes because they resume execution immediately after their I/O finishes. However, it may interrupt CPU-bound processes more frequently.-I IO RUN LATER:
This allows the current CPU-bound process to continue running uninterrupted, potentially improving throughput for CPU-bound workloads but slowing down I/O-bound processes.-S SWITCH ON IO:
This leads to more efficient use of CPU resources because the CPU will continue running another process while waiting for I/O-bound processes to complete their I/O operations.-S SWITCH ON END:
This may lead to wasted CPU time when the process is blocked on I/O, reducing overall efficiency.
| Flag S | Flag I | Time (Seed 1) | Time (Seed 2) | Time (Seed 3) | Average Time |
|---|---|---|---|---|---|
| SWITCH ON IO | RUN IMMEDIATE | 15 | 16 | 17 | 16 |
| SWITCH ON IO | RUN LATER | 15 | 16 | 18 | 16.3 |
| SWITCH ON END | RUN IMMEDIATE | 18 | 30 | 24 | 24 |
| SWITCH ON END | RUN LATER | 18 | 30 | 24 | 24 |