/xv6-updated

Primary LanguageCOtherNOASSERTION

Assignment - 4 : xv6

Spec1

strace() syscall:

  • Made required changes to the following files to add the syscall:
  1. syscall.h
  2. defs.h
  3. user.h
  4. sysproc.c
  5. usys.S
  6. syscall.c

  • Added rtime, stime, etime in struct proc.

  • There values update acccording to clockitr().

  • Added strace.c user program in user and Makefile.

Schedulers:

Added SCHEDULER object in Makefile.

FCFS

  • Iterate over all processes and select the one with lowest creation time which has status RUNNABLE.

PBS

  • Added priority and niceness in struct proc.

  • Process is selected according to the defined Dynamic Priority.

  • After process is scheduled, niceness is updated according to runtime and waiting time for the process.

  • Added set_priority syscall to change the static priority of the process.

  • Added setpriority user program in the user and Makefile.

MLFQ

  • Added queue_priority to store current queue priority.

  • mlfq_init(), initializes the required values of queues.

  • push(proc, pr), pushes the given proc into the queue whose number is pr.

  • pop(proc, pr), removes the given proc from the queue whose number is pr and shifts the PBCs coming after it one step to the left.

  • We iterate over all process and select the first process with hight priority. And then implement different time slices for different queues.

  • Aging and starvation is also implemented for this.

How could this be exploited by a process (MLFQ)?

  • If a process gives up CPU before MAX_AGE, it will not demote to lower priority.

  • Thus proccesses can just preempt themselves just before max_age and add themselves to queue again.

  • This explotation keeps the process in priority 0, forever.

Comparison:

  • DEFAULT (RR):

Total rtime: 189, Total wtime: 1171

Average rtime: 18, Average wtime: 117

  • FCFS

Total rtime: 449, Total wtime: 547

Average rtime: 44, Average wtime: 54

  • PBS

Total rtime: 244, Total wtime: 1084

Average rtime: 24, Average wtime: 108