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authorrsc <rsc>2006-07-16 01:15:28 +0000
committerrsc <rsc>2006-07-16 01:15:28 +0000
commit65bd8e139a8368e987455a10ec59dd7b079b3af1 (patch)
tree8ce996135fadab4abde8acf5a6ed4eb69d463c60 /proc.c
parent40a2a08319511fd157d2d77eefbda52423cc81ec (diff)
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New scheduler.
Removed cli and sti stack in favor of tracking number of locks held on each CPU and explicit conditionals in spinlock.c.
Diffstat (limited to 'proc.c')
-rw-r--r--proc.c321
1 files changed, 168 insertions, 153 deletions
diff --git a/proc.c b/proc.c
index 76ec64e..01d8f2f 100644
--- a/proc.c
+++ b/proc.c
@@ -12,6 +12,7 @@ struct spinlock proc_table_lock;
struct proc proc[NPROC];
struct proc *curproc[NCPU];
int next_pid = 1;
+extern void forkret(void);
/*
* set up a process's task state and segment descriptors
@@ -96,12 +97,14 @@ newproc()
*(np->tf) = *(op->tf);
np->tf->tf_regs.reg_eax = 0; // so fork() returns 0 in child
- // set up new jmpbuf to start executing at trapret with esp pointing at tf
+ // Set up new jmpbuf to start executing forkret (see trapasm.S)
+ // with esp pointing at tf. Forkret will call forkret1 (below) to release
+ // the proc_table_lock and then jump into the usual trap return code.
memset(&np->jmpbuf, 0, sizeof np->jmpbuf);
- np->jmpbuf.jb_eip = (unsigned) trapret;
+ np->jmpbuf.jb_eip = (unsigned) forkret;
np->jmpbuf.jb_esp = (unsigned) np->tf - 4; // -4 for the %eip that isn't actually there
- // copy file descriptors
+ // Copy file descriptors
for(fd = 0; fd < NOFILE; fd++){
np->fds[fd] = op->fds[fd];
if(np->fds[fd])
@@ -112,127 +115,152 @@ newproc()
}
void
+forkret1(void)
+{
+ release(&proc_table_lock);
+}
+
+// Per-CPU process scheduler.
+// Each CPU calls scheduler() after setting itself up.
+// Scheduler never returns. It loops, doing:
+// - choose a process to run
+// - longjmp to start running that process
+// - eventually that process transfers control back
+// via longjmp back to the top of scheduler.
+void
scheduler(void)
{
- struct proc *op, *np;
+ struct proc *p;
int i;
cprintf("start scheduler on cpu %d jmpbuf %p\n", cpu(), &cpus[cpu()].jmpbuf);
cpus[cpu()].lastproc = &proc[0];
- setjmp(&cpus[cpu()].jmpbuf);
-
- op = curproc[cpu()];
-
- if(op == 0 || op->mtx != &proc_table_lock)
- acquire1(&proc_table_lock, op);
-
- if(op){
- if(op->newstate <= 0 || op->newstate > ZOMBIE)
- panic("scheduler");
- op->state = op->newstate;
- op->newstate = -1;
- if(op->mtx){
- struct spinlock *mtx = op->mtx;
- op->mtx = 0;
- if(mtx != &proc_table_lock)
- release1(mtx, op);
- }
- }
-
- // find a runnable process and switch to it
- curproc[cpu()] = 0;
- np = cpus[cpu()].lastproc + 1;
- while(1){
+ for(;;){
+ // Loop over process table looking for process to run.
+ acquire(&proc_table_lock);
for(i = 0; i < NPROC; i++){
- if(np >= &proc[NPROC])
- np = &proc[0];
- if(np->state == RUNNABLE)
- break;
- np++;
- }
-
- if(i < NPROC){
- np->state = RUNNING;
- release1(&proc_table_lock, op);
- break;
+ p = &proc[i];
+ if(p->state != RUNNABLE)
+ continue;
+
+ // Run this process.
+ // XXX move this into swtch or trapret or something.
+ // It can run on the other stack.
+ // h/w sets busy bit in TSS descriptor sometimes, and faults
+ // if it's set in LTR. so clear tss descriptor busy bit.
+ p->gdt[SEG_TSS].sd_type = STS_T32A;
+
+ // XXX should probably have an lgdt() function in x86.h
+ // to confine all the inline assembly.
+ // XXX probably ought to lgdt on trap return too, in case
+ // a system call has moved a program or changed its size.
+ asm volatile("lgdt %0" : : "g" (p->gdt_pd.pd_lim));
+ ltr(SEG_TSS << 3);
+
+ // Switch to chosen process. It is the process's job
+ // to release proc_table_lock and then reacquire it
+ // before jumping back to us.
+ if(0) cprintf("cpu%d: run %d\n", cpu(), p-proc);
+ curproc[cpu()] = p;
+ p->state = RUNNING;
+ if(setjmp(&cpus[cpu()].jmpbuf) == 0)
+ longjmp(&p->jmpbuf);
+
+ // Process is done running for now.
+ // It should have changed its p->state before coming back.
+ curproc[cpu()] = 0;
+ if(p->state == RUNNING)
+ panic("swtch to scheduler with state=RUNNING");
+
+ // XXX if not holding proc_table_lock panic.
}
+ release(&proc_table_lock);
- release1(&proc_table_lock, op);
- op = 0;
- acquire(&proc_table_lock);
- np = &proc[0];
+ if(cpus[cpu()].nlock != 0)
+ panic("holding locks in scheduler");
+
+ // With proc_table_lock released, there are no
+ // locks held on this cpu, so interrupts are enabled.
+ // Hardware interrupts can happen here.
+ // Also, releasing the lock here lets the other CPUs
+ // look for runnable processes too.
}
+}
- cpus[cpu()].lastproc = np;
- curproc[cpu()] = np;
-
- // h/w sets busy bit in TSS descriptor sometimes, and faults
- // if it's set in LTR. so clear tss descriptor busy bit.
- np->gdt[SEG_TSS].sd_type = STS_T32A;
-
- // XXX should probably have an lgdt() function in x86.h
- // to confine all the inline assembly.
- // XXX probably ought to lgdt on trap return too, in case
- // a system call has moved a program or changed its size.
- asm volatile("lgdt %0" : : "g" (np->gdt_pd.pd_lim));
- ltr(SEG_TSS << 3);
-
- if(0) cprintf("cpu%d: run %d esp=%p callerpc=%p\n", cpu(), np-proc);
- longjmp(&np->jmpbuf);
+// Enter scheduler. Must already hold proc_table_lock
+// and have changed curproc[cpu()]->state.
+void
+sched(void)
+{
+ if(setjmp(&curproc[cpu()]->jmpbuf) == 0)
+ longjmp(&cpus[cpu()].jmpbuf);
}
-// give up the cpu by switching to the scheduler,
-// which runs on the per-cpu stack.
+// Give up the CPU for one scheduling round.
void
-swtch(int newstate)
+yield()
{
- struct proc *p = curproc[cpu()];
+ struct proc *p;
- if(p == 0)
- panic("swtch no proc");
- if(p->mtx == 0 && p->locks != 0)
- panic("swtch w/ locks");
- if(p->mtx && p->locks != 1)
- panic("swtch w/ locks 1");
- if(p->mtx && p->mtx->locked == 0)
- panic("switch w/ lock but not held");
- if(p->locks && (read_eflags() & FL_IF))
- panic("swtch w/ lock but FL_IF");
-
- p->newstate = newstate; // basically an argument to scheduler()
- if(setjmp(&p->jmpbuf) == 0)
- longjmp(&cpus[cpu()].jmpbuf);
+ if((p=curproc[cpu()]) == 0 || curproc[cpu()]->state != RUNNING)
+ panic("yield");
+ acquire(&proc_table_lock);
+ p->state = RUNNABLE;
+ sched();
+ release(&proc_table_lock);
}
+// Atomically release lock and sleep on chan.
+// Reacquires lock when reawakened.
void
-sleep(void *chan, struct spinlock *mtx)
+sleep(void *chan, struct spinlock *lk)
{
struct proc *p = curproc[cpu()];
if(p == 0)
panic("sleep");
+ // Must acquire proc_table_lock in order to
+ // change p->state and then call sched.
+ // Once we hold proc_table_lock, we can be
+ // guaranteed that we won't miss any wakeup
+ // (wakeup runs with proc_table_lock locked),
+ // so it's okay to release lk.
+ if(lk != &proc_table_lock){
+ acquire(&proc_table_lock);
+ release(lk);
+ }
+
+ // Go to sleep.
p->chan = chan;
- p->mtx = mtx; // scheduler will release it
+ p->state = SLEEPING;
+ sched();
- swtch(WAITING);
-
- if(mtx)
- acquire(mtx);
+ // Tidy up.
p->chan = 0;
+
+ // Reacquire original lock.
+ if(lk != &proc_table_lock){
+ release(&proc_table_lock);
+ acquire(lk);
+ }
}
+// Wake up all processes sleeping on chan.
+// Proc_table_lock must be held.
void
wakeup1(void *chan)
{
struct proc *p;
for(p = proc; p < &proc[NPROC]; p++)
- if(p->state == WAITING && p->chan == chan)
+ if(p->state == SLEEPING && p->chan == chan)
p->state = RUNNABLE;
}
+// Wake up all processes sleeping on chan.
+// Proc_table_lock is acquired and released.
void
wakeup(void *chan)
{
@@ -241,15 +269,32 @@ wakeup(void *chan)
release(&proc_table_lock);
}
-// give up the CPU but stay marked as RUNNABLE
-void
-yield()
+// Kill the process with the given pid.
+// Process won't actually exit until it returns
+// to user space (see trap in trap.c).
+int
+proc_kill(int pid)
{
- if(curproc[cpu()] == 0 || curproc[cpu()]->state != RUNNING)
- panic("yield");
- swtch(RUNNABLE);
+ struct proc *p;
+
+ acquire(&proc_table_lock);
+ for(p = proc; p < &proc[NPROC]; p++){
+ if(p->pid == pid){
+ p->killed = 1;
+ // Wake process from sleep if necessary.
+ if(p->state == SLEEPING)
+ p->state = RUNNABLE;
+ release(&proc_table_lock);
+ return 0;
+ }
+ }
+ release(&proc_table_lock);
+ return -1;
}
+// Exit the current process. Does not return.
+// Exited processes remain in the zombie state
+// until their parent calls wait() to find out they exited.
void
proc_exit()
{
@@ -257,6 +302,7 @@ proc_exit()
struct proc *cp = curproc[cpu()];
int fd;
+ // Close all open files.
for(fd = 0; fd < NOFILE; fd++){
if(cp->fds[fd]){
fd_close(cp->fds[fd]);
@@ -266,91 +312,60 @@ proc_exit()
acquire(&proc_table_lock);
- // wake up parent
+ // Wake up our parent.
for(p = proc; p < &proc[NPROC]; p++)
if(p->pid == cp->ppid)
wakeup1(p);
- // abandon children
+ // Reparent our children to process 1.
for(p = proc; p < &proc[NPROC]; p++)
if(p->ppid == cp->pid)
- p->pid = 1;
+ p->ppid = 1;
- cp->mtx = &proc_table_lock;
- swtch(ZOMBIE);
- panic("a zombie revived");
+ // Jump into the scheduler, never to return.
+ cp->state = ZOMBIE;
+ sched();
+ panic("zombie exit");
}
+// Wait for a child process to exit and return its pid.
+// Return -1 if this process has no children.
int
proc_wait(void)
{
struct proc *p;
struct proc *cp = curproc[cpu()];
- int any, pid;
+ int i, havekids, pid;
acquire(&proc_table_lock);
-
- while(1){
- any = 0;
- for(p = proc; p < &proc[NPROC]; p++){
- if(p->state == ZOMBIE && p->ppid == cp->pid){
- kfree(p->mem, p->sz);
- kfree(p->kstack, KSTACKSIZE);
- pid = p->pid;
- p->state = UNUSED;
- release(&proc_table_lock);
- return pid;
+ for(;;){
+ // Scan through table looking zombie children.
+ havekids = 0;
+ for(i = 0; i < NPROC; i++){
+ p = &proc[i];
+ if(p->ppid == cp->pid){
+ if(p->state == ZOMBIE){
+ // Found one.
+ kfree(p->mem, p->sz);
+ kfree(p->kstack, KSTACKSIZE);
+ pid = p->pid;
+ p->state = UNUSED;
+ p->pid = 0;
+ release(&proc_table_lock);
+ return pid;
+ }
+ havekids = 1;
}
- if(p->state != UNUSED && p->ppid == cp->pid)
- any = 1;
}
- if(any == 0){
+
+ // No point waiting if we don't have any children.
+ if(!havekids){
release(&proc_table_lock);
return -1;
}
+
+ // Wait for children to exit. (See wakeup1 call in proc_exit.)
sleep(cp, &proc_table_lock);
}
}
-int
-proc_kill(int pid)
-{
- struct proc *p;
-
- acquire(&proc_table_lock);
- for(p = proc; p < &proc[NPROC]; p++){
- if(p->pid == pid && p->state != UNUSED){
- p->killed = 1;
- if(p->state == WAITING)
- p->state = RUNNABLE;
- release(&proc_table_lock);
- return 0;
- }
- }
- release(&proc_table_lock);
- return -1;
-}
-
-// disable interrupts
-void
-cli(void)
-{
- if(cpus[cpu()].clis == 0)
- __asm __volatile("cli");
- cpus[cpu()].clis += 1;
- if((read_eflags() & FL_IF) != 0)
- panic("cli but enabled");
-}
-
-// enable interrupts
-void
-sti(void)
-{
- if((read_eflags() & FL_IF) != 0)
- panic("sti but enabled");
- if(cpus[cpu()].clis < 1)
- panic("sti");
- cpus[cpu()].clis -= 1;
- if(cpus[cpu()].clis < 1)
- __asm __volatile("sti");
-}