[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v9 03/19] qspinlock: Add pending bit
On Thu, Apr 17, 2014 at 11:03:55AM -0400, Waiman Long wrote: > +/** > + * trylock_pending - try to acquire queue spinlock using the pending bit > + * @lock : Pointer to queue spinlock structure > + * @pval : Pointer to value of the queue spinlock 32-bit word > + * Return: 1 if lock acquired, 0 otherwise > + */ > +static inline int trylock_pending(struct qspinlock *lock, u32 *pval) > +{ > + u32 old, new, val = *pval; I'm not thrilled about you breaking this into a separate function; the compiler will put it right back and now you get to have that ugly pointer stuff. It also makes the function control flow not match the state diagram anymore. > + > + /* > + * trylock || pending > + * > + * 0,0,0 -> 0,0,1 ; trylock > + * 0,0,1 -> 0,1,1 ; pending > + */ > + for (;;) { > + /* > + * If we observe any contention; queue. > + */ > + if (val & ~_Q_LOCKED_MASK) > + return 0; > + > + new = _Q_LOCKED_VAL; > + if (val == new) > + new |= _Q_PENDING_VAL; > + > + old = atomic_cmpxchg(&lock->val, val, new); > + if (old == val) > + break; > + > + *pval = val = old; > + } > + > + /* > + * we won the trylock > + */ > + if (new == _Q_LOCKED_VAL) > + return 1; > + > + /* > + * we're pending, wait for the owner to go away. > + * > + * *,1,1 -> *,1,0 > + */ > + while ((val = atomic_read(&lock->val)) & _Q_LOCKED_MASK) > + arch_mutex_cpu_relax(); That was a cpu_relax(). > + > + /* > + * take ownership and clear the pending bit. > + * > + * *,1,0 -> *,0,1 > + */ > + for (;;) { > + new = (val & ~_Q_PENDING_MASK) | _Q_LOCKED_VAL; > + > + old = atomic_cmpxchg(&lock->val, val, new); > + if (old == val) > + break; > + > + val = old; > + } > + return 1; > +} _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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