/*------------------------------------------------------------------------
* resched -- reschedule processor to highest priority ready process
*
* Notes: Upon entry, currpid gives current process id.
* Proctab[currpid].pstate gives correct NEXT state for
* current process if other than PRREADY.
*------------------------------------------------------------------------
*/
int resched()
{
STATWORD PS;
register struct pentry *optr; /* pointer to old process entry */
register struct pentry *nptr; /* pointer to new process entry */
disable(PS);
/* no switch needed if current process priority higher than next*/
if ( ( (optr= &proctab[currpid])->pstate == PRCURR) &&
(lastkey(rdytail)<optr->pprio)) {
restore(PS);
return(OK);
}
#ifdef STKCHK
/* make sure current stack has room for ctsw */
asm("movl %esp, currSP");
if (currSP - optr->plimit < 48) {
kprintf("Bad SP current process, pid=%d (%s), lim=0x%lx, currently 0x%lx\n",
currpid, optr->pname,
(unsigned long) optr->plimit,
(unsigned long) currSP);
panic("current process stack overflow");
}
#endif
/* force context switch */
if (optr->pstate == PRCURR) {
optr->pstate = PRREADY;
insert(currpid,rdyhead,optr->pprio);
}
/* remove highest priority process at end of ready list */
nptr = &proctab[ (currpid = getlast(rdytail)) ];
nptr->pstate = PRCURR; /* mark it currently running */
#ifdef notdef
#ifdef STKCHK
if ( *( (int *)nptr->pbase ) != MAGIC ) {
kprintf("Bad magic pid=%d value=0x%lx, at 0x%lx\n",
currpid,
(unsigned long) *( (int *)nptr->pbase ),
(unsigned long) nptr->pbase);
panic("stack corrupted");
}
/*
* need ~16 longs of stack space below, so include that in check
* below.
*/
if (nptr->pesp - nptr->plimit < 48) {
kprintf("Bad SP pid=%d (%s), lim=0x%lx will be 0x%lx\n",
currpid, nptr->pname,
(unsigned long) nptr->plimit,
(unsigned long) nptr->pesp);
panic("stack overflow");
}
#endif /* STKCHK */
#endif /* notdef */
#ifdef RTCLOCK
preempt = QUANTUM; /* reset preemption counter */
#endif
#ifdef DEBUG
PrintSaved(nptr);
#endif
// When performing a context switch between processes we must also
// switch between memory spaces. This is accomplished by adjusting
// the PDBR register with every context switch.
//
// 5 - Context switch
// - every process has separate page directory
// - before ctxsw() load CR3 with the process' PDBR
set_PDBR(VA2VPNO(nptr->pd));
#if DUSTYDEBUG
kprintf("switching to process %d\n", (nptr - proctab));
#endif
ctxsw(&optr->pesp, optr->pirmask, &nptr->pesp, nptr->pirmask);
#ifdef DEBUG
PrintSaved(nptr);
#endif
/* The OLD process returns here when resumed. */
restore(PS);
return OK;
}
/*------------------------------------------------------------------------
* resched -- reschedule processor to highest priority ready process
*
* Notes: Upon entry, currpid gives current process id.
* Proctab[currpid].pstate gives correct NEXT state for
* current process if other than PRREADY.
*------------------------------------------------------------------------
*/
int resched()
{
STATWORD PS;
register struct pentry *optr; /* pointer to old process entry */
register struct pentry *nptr; /* pointer to new process entry */
register int i;
disable(PS);
/* no switch needed if current process priority higher than next*/
if ( ( (optr= &proctab[currpid])->pstate == PRCURR) &&
(lastkey(rdytail)<optr->pprio)) {
restore(PS);
return(OK);
}
#ifdef STKCHK
/* make sure current stack has room for ctsw */
asm("movl %esp, currSP");
if (currSP - optr->plimit < 48) {
kprintf("Bad SP current process, pid=%d (%s), lim=0x%lx, currently 0x%lx\n",
currpid, optr->pname,
(unsigned long) optr->plimit,
(unsigned long) currSP);
panic("current process stack overflow");
}
#endif
/* force context switch */
if (optr->pstate == PRCURR) {
optr->pstate = PRREADY;
insert(currpid,rdyhead,optr->pprio);
}
/* remove highest priority process at end of ready list */
nptr = &proctab[ (currpid = getlast(rdytail)) ];
nptr->pstate = PRCURR; /* mark it currently running */
#ifdef notdef
#ifdef STKCHK
if ( *( (int *)nptr->pbase ) != MAGIC ) {
kprintf("Bad magic pid=%d value=0x%lx, at 0x%lx\n",
currpid,
(unsigned long) *( (int *)nptr->pbase ),
(unsigned long) nptr->pbase);
panic("stack corrupted");
}
/*
* need ~16 longs of stack space below, so include that in check
* below.
*/
if (nptr->pesp - nptr->plimit < 48) {
kprintf("Bad SP pid=%d (%s), lim=0x%lx will be 0x%lx\n",
currpid, nptr->pname,
(unsigned long) nptr->plimit,
(unsigned long) nptr->pesp);
panic("stack overflow");
}
#endif /* STKCHK */
#endif /* notdef */
#ifdef RTCLOCK
preempt = QUANTUM; /* reset preemption counter */
#endif
#ifdef DEBUG
PrintSaved(nptr);
#endif
//OS proj 3 modify
write_cr3(nptr->pdbr);
ctxsw(&optr->pesp, optr->pirmask, &nptr->pesp, nptr->pirmask);
#ifdef DEBUG
PrintSaved(nptr);
#endif
/* The OLD process returns here when resumed. */
restore(PS);
return OK;
}
