static inline bool pv_queued_spin_steal_lock(struct qspinlock *lock)
{
struct __qspinlock *l = (void *)lock;
- int ret = !(atomic_read(&lock->val) & _Q_LOCKED_PENDING_MASK) &&
- (cmpxchg(&l->locked, 0, _Q_LOCKED_VAL) == 0);
- qstat_inc(qstat_pv_lock_stealing, ret);
- return ret;
+ if (!(atomic_read(&lock->val) & _Q_LOCKED_PENDING_MASK) &&
+ (cmpxchg(&l->locked, 0, _Q_LOCKED_VAL) == 0)) {
+ qstat_inc(qstat_pv_lock_stealing, true);
+ return true;
+ }
+
+ return false;
}
/*
static inline bool
pv_wait_early(struct pv_node *prev, int loop)
{
-
if ((loop & PV_PREV_CHECK_MASK) != 0)
return false;
{
struct pv_node *pn = (struct pv_node *)node;
struct pv_node *pp = (struct pv_node *)prev;
- int waitcnt = 0;
int loop;
bool wait_early;
- /* waitcnt processing will be compiled out if !QUEUED_LOCK_STAT */
- for (;; waitcnt++) {
+ for (;;) {
for (wait_early = false, loop = SPIN_THRESHOLD; loop; loop--) {
if (READ_ONCE(node->locked))
return;
if (!READ_ONCE(node->locked)) {
qstat_inc(qstat_pv_wait_node, true);
- qstat_inc(qstat_pv_wait_again, waitcnt);
qstat_inc(qstat_pv_wait_early, wait_early);
pv_wait(&pn->state, vcpu_halted);
}
pv_wait(&l->locked, _Q_SLOW_VAL);
/*
- * The unlocker should have freed the lock before kicking the
- * CPU. So if the lock is still not free, it is a spurious
- * wakeup or another vCPU has stolen the lock. The current
- * vCPU should spin again.
+ * Because of lock stealing, the queue head vCPU may not be
+ * able to acquire the lock before it has to wait again.
*/
- qstat_inc(qstat_pv_spurious_wakeup, READ_ONCE(l->locked));
}
/*
* unhash. Otherwise it would be possible to have multiple @lock
* entries, which would be BAD.
*/
- locked = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0);
+ locked = cmpxchg_release(&l->locked, _Q_LOCKED_VAL, 0);
if (likely(locked == _Q_LOCKED_VAL))
return;