diff options
Diffstat (limited to 'kernel/spinlock.c')
| -rw-r--r-- | kernel/spinlock.c | 13 |
1 files changed, 6 insertions, 7 deletions
diff --git a/kernel/spinlock.c b/kernel/spinlock.c index 5a44a46..83512bb 100644 --- a/kernel/spinlock.c +++ b/kernel/spinlock.c @@ -18,8 +18,6 @@ initlock(struct spinlock *lk, char *name) // Acquire the lock. // Loops (spins) until the lock is acquired. -// Holding a lock for a long time may cause -// other CPUs to waste time spinning to acquire it. void acquire(struct spinlock *lk) { @@ -27,7 +25,7 @@ acquire(struct spinlock *lk) if(holding(lk)) panic("acquire"); - // On RISC-V, this turns into an atomic swap: + // On RISC-V, sync_lock_test_and_set turns into an atomic swap: // a5 = 1 // s1 = &lk->locked // amoswap.w.aq a5, a5, (s1) @@ -59,9 +57,10 @@ release(struct spinlock *lk) __sync_synchronize(); // Release the lock, equivalent to lk->locked = 0. - // This code can't use a C assignment, since it might - // not be atomic. - // On RISC-V, this turns into an atomic swap: + // 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); @@ -81,7 +80,7 @@ holding(struct spinlock *lk) } // push_off/pop_off are like intr_off()/intr_on() except that they are matched: -// it takes two pop_off to undo two push_off. Also, if interrupts +// 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 |