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// Mutual exclusion spin locks.
#include "types.h"
#include "param.h"
#include "memlayout.h"
#include "spinlock.h"
#include "riscv.h"
#include "proc.h"
#include "defs.h"
#ifdef LAB_LOCK
#define NLOCK 500
static struct spinlock *locks[NLOCK];
struct spinlock lock_locks;
void
freelock(struct spinlock *lk)
{
acquire(&lock_locks);
int i;
for (i = 0; i < NLOCK; i++) {
if(locks[i] == lk) {
locks[i] = 0;
break;
}
}
release(&lock_locks);
}
static void
findslot(struct spinlock *lk) {
acquire(&lock_locks);
int i;
for (i = 0; i < NLOCK; i++) {
if(locks[i] == 0) {
locks[i] = lk;
release(&lock_locks);
return;
}
}
panic("findslot");
}
#endif
void
initlock(struct spinlock *lk, char *name)
{
lk->name = name;
lk->locked = 0;
lk->cpu = 0;
#ifdef LAB_LOCK
lk->nts = 0;
lk->n = 0;
findslot(lk);
#endif
}
// Acquire the lock.
// Loops (spins) until the lock is acquired.
void
acquire(struct spinlock *lk)
{
push_off(); // disable interrupts to avoid deadlock.
if(holding(lk))
panic("acquire");
#ifdef LAB_LOCK
__sync_fetch_and_add(&(lk->n), 1);
#endif
// On RISC-V, sync_lock_test_and_set turns into an atomic swap:
// a5 = 1
// s1 = &lk->locked
// amoswap.w.aq a5, a5, (s1)
while(__sync_lock_test_and_set(&lk->locked, 1) != 0) {
#ifdef LAB_LOCK
__sync_fetch_and_add(&(lk->nts), 1);
#else
;
#endif
}
// Tell the C compiler and the processor to not move loads or stores
// past this point, to ensure that the critical section's memory
// references happen strictly after the lock is acquired.
// On RISC-V, this emits a fence instruction.
__sync_synchronize();
// Record info about lock acquisition for holding() and debugging.
lk->cpu = mycpu();
}
// Release the lock.
void
release(struct spinlock *lk)
{
if(!holding(lk))
panic("release");
lk->cpu = 0;
// Tell the C compiler and the CPU to not move loads or stores
// past this point, to ensure that all the stores in the critical
// section are visible to other CPUs before the lock is released,
// and that loads in the critical section occur strictly before
// the lock is released.
// On RISC-V, this emits a fence instruction.
__sync_synchronize();
// Release the lock, equivalent to lk->locked = 0.
// This code doesn't use a C assignment, since the C standard
// implies that an assignment might be implemented with
// multiple store instructions.
// On RISC-V, sync_lock_release turns into an atomic swap:
// s1 = &lk->locked
// amoswap.w zero, zero, (s1)
__sync_lock_release(&lk->locked);
pop_off();
}
// Check whether this cpu is holding the lock.
// Interrupts must be off.
int
holding(struct spinlock *lk)
{
int r;
r = (lk->locked && lk->cpu == mycpu());
return r;
}
// push_off/pop_off are like intr_off()/intr_on() except that they are matched:
// it takes two pop_off()s to undo two push_off()s. Also, if interrupts
// are initially off, then push_off, pop_off leaves them off.
void
push_off(void)
{
int old = intr_get();
intr_off();
if(mycpu()->noff == 0)
mycpu()->intena = old;
mycpu()->noff += 1;
}
void
pop_off(void)
{
struct cpu *c = mycpu();
if(intr_get())
panic("pop_off - interruptible");
if(c->noff < 1)
panic("pop_off");
c->noff -= 1;
if(c->noff == 0 && c->intena)
intr_on();
}
// Read a shared 32-bit value without holding a lock
int
atomic_read4(int *addr) {
uint32 val;
__atomic_load(addr, &val, __ATOMIC_SEQ_CST);
return val;
}
#ifdef LAB_LOCK
int
snprint_lock(char *buf, int sz, struct spinlock *lk)
{
int n = 0;
if(lk->n > 0) {
n = snprintf(buf, sz, "lock: %s: #test-and-set %d #acquire() %d\n",
lk->name, lk->nts, lk->n);
}
return n;
}
int
statslock(char *buf, int sz) {
int n;
int tot = 0;
acquire(&lock_locks);
n = snprintf(buf, sz, "--- lock kmem/bcache stats\n");
for(int i = 0; i < NLOCK; i++) {
if(locks[i] == 0)
break;
if(strncmp(locks[i]->name, "bcache", strlen("bcache")) == 0 ||
strncmp(locks[i]->name, "kmem", strlen("kmem")) == 0) {
tot += locks[i]->nts;
n += snprint_lock(buf +n, sz-n, locks[i]);
}
}
n += snprintf(buf+n, sz-n, "--- top 5 contended locks:\n");
int last = 100000000;
// stupid way to compute top 5 contended locks
for(int t = 0; t < 5; t++) {
int top = 0;
for(int i = 0; i < NLOCK; i++) {
if(locks[i] == 0)
break;
if(locks[i]->nts > locks[top]->nts && locks[i]->nts < last) {
top = i;
}
}
n += snprint_lock(buf+n, sz-n, locks[top]);
last = locks[top]->nts;
}
n += snprintf(buf+n, sz-n, "tot= %d\n", tot);
release(&lock_locks);
return n;
}
#endif
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