IIT_xv6_Labs: Process Management

https://www.cse.iitb.ac.in/~mythili/os/labs/lab-xv6-proc/xv6-proc.pdf

ProcessInfo systemcall Implementation

to record number of number of times the process was context switched in by the scheduler, add a field to the proc structure.
proc.h

 37 // Per-process state
 38 struct proc {
 53   int cscnt;                    //number of context switched
 54 };

First, allocproc() have to initialize the cscnt as 0.
Then, every time that the process is scheduled, scheduler will increment the cscnt.
proc.c

74 static struct proc*
 75 allocproc(void)
 ...
 89 found:
 90   p->state = EMBRYO;
 91   p->pid = nextpid++;
 92   p->cscnt = 0; //initialization

324 void
325 scheduler(void)
326 {
...
337     for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
338       if(p->state != RUNNABLE)
339         continue;
...
344       c->proc = p;
345       switchuvm(p);
346       p->state = RUNNING;
347       p->cscnt++; 

function getProcInfo() was implemented as follows:
PID 1, init process has no parent field, and thus it would cause segmentation fault without exception.
-> parent pid of the init process is set as 0 by convention.
proc.c

665 int getProcInfo(int pid, struct processInfo *pinfo) {
666
667  struct proc *p;
668
669   acquire(&ptable.lock);
670   for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
671     if(p->pid == pid){
672       if(pid == 1) pinfo->ppid = 0; //parent pid of the init process is 0 by convention
673       else  pinfo->ppid = p->parent->pid;
674       pinfo->psize = p->sz;
675       pinfo->numberContextSwitches = p->cscnt;
676       release(&ptable.lock);
677       return 0;
678     }
679   }
680       release(&ptable.lock);
681       return -1;
682
683 }

Weighted Round Robin Implementation

A process with high priority should be given more time slices than others.

trap.c

104   // Force process to give up CPU on clock tick.
105   // If interrupts were on while locks held, would need to check nlock.
106   if(myproc() && myproc()->state == RUNNING &&
107      tf->trapno == T_IRQ0+IRQ_TIMER) {
108     current = myproc()->currentprio;
109     if(current > 0) {
110       myproc()->currentprio = current-1;
111     }
112
113     else  {
114     yield();
115     }
116   }

A “welcoming” fork

child process must executes a function specified by a parent process.
To inform the child process to begin execution at the specific function, I set the "wf" in the struct proc and "fnc" field.

proc.h

38 struct proc {
 ...
 56   int wf;                       //welcome function 0 / 1
 57   uint fnc;                     //address of welcome function
 58 };

proc.c

184 int
185 fork(void)
186 {
...
207   if(curproc->wf) {
208     np->tf->eip = curproc->fnc; //if the welcomefunction is enabled, set the instruction p
    ointer to function address
209    }
...

704 void welcomeFunction(void(*fnc) (void)) {
705     struct proc *curproc = myproc();
706
707     curproc->wf = 1;
708     curproc->fnc = (uint)fnc;
709
710 }
711
712 int welcomeDone(void) {
713   struct proc *curproc = myproc();
714   curproc->tf->eip = curproc->parent->tf->eip;
715   // child process must return 0 from fork() function.
716   return 0; //this must be set because %eax will be set by syscall return value. -> 161 line of syscall.c, if return is void, %eax will be set to unknown value and test code cannot recognize the child process.
717 }

https://www.cse.iitb.ac.in/~mythili/os/labs/lab-xv6-mem/xv6-mem.pdf
https://www.cse.iitb.ac.in/~mythili/os/labs/lab-xv6-sync/xv6-sync.pdf