Schedulling algorithm cpu time

Question

I am trying to make a simulator for a scheduling algorithm in C using round robin and fcfs.

I just have a few questions as I have tried to look it up and read the kernel commands but im still that confused :( This program is being done on putty(linux) where you have a list of processes with a time clock that execute or take up cpu time.

1. How do we make a process take up CPU time? Do we call the sys() function(don't know which one) or are we meant to malloc a process when I read it in my program from a textfile? I know i may sound stupid, but please explain.

2. What do you suggest is the best data structure to use for the storage of the process(time created,process id,memory size,job time) for ex (0,2,70,8)?

3. When a process finishes in its job time, how do we terminate it for it to free itself from the CPU to ensure the other process at a clock time after it can use the cpu?

4. How do you implement the clock time, is there any inbuilt function or to just use a for loop.

I hope these are not asking too many questions but whoever can get back to me I would really appreciate it.

Regards

Answer 1

If you're building a simulator you should NOT be actually waiting that amount of time, you should "schedule" by updating counters and saying process p1 has run for 750ms total so far, scheduled 3 times for 250ms, 250ms, 250ms, etc... Trying to attempt to run a scheduling simulation in real time in user space is bound to give you odd results as your process itself needs to be scheduled as well.

For instance, if you want to simulate FCFS, you implement a simple "process" queue and give them each a time slice (you can use the default kernel timeslice or your own, doesn't really matter) and each of these processes will have some total execution time to finish and you can do calculations based off this. For example P1 is a process, requires 3.12 seconds of CPU time to finish (I don't think memory simulation is needed since we're doing scheduling and not caching or anything else taken into account). You just run the algorithm like you normally would but just adding numbers, so you "run" P1, add time to its counter and check if it's done. If it is check the difference etc... and you can keep a global time to keep track of how long it has run in wall clock time. Then simply put P1 at the end of the queue and "schedule" the next process.

Now if you want to measure scheduling performance that's completely different and this usually involves running workload benchmarks to run many processes on the system and check overall performance metrics for each.