Messages in this thread | | | Date | Thu, 17 Apr 2014 17:46:27 -0400 | From | Waiman Long <> | Subject | Re: [PATCH v9 05/19] qspinlock: Optimize for smaller NR_CPUS |
| |
On 04/17/2014 11:56 AM, Peter Zijlstra wrote: > On Thu, Apr 17, 2014 at 11:03:57AM -0400, Waiman Long wrote: >> +struct __qspinlock { >> + union { >> + atomic_t val; >> + struct { >> +#ifdef __LITTLE_ENDIAN >> + u16 locked_pending; >> + u16 tail; >> +#else >> + u16 tail; >> + u16 locked_pending; >> +#endif >> + }; >> + }; >> +}; >> + >> +/** >> + * clear_pending_set_locked - take ownership and clear the pending bit. >> + * @lock: Pointer to queue spinlock structure >> + * @val : Current value of the queue spinlock 32-bit word >> + * >> + * *,1,0 -> *,0,1 >> + */ >> +static __always_inline void >> +clear_pending_set_locked(struct qspinlock *lock, u32 val) >> +{ >> + struct __qspinlock *l = (void *)lock; >> + >> + ACCESS_ONCE(l->locked_pending) = 1; > You lost the __constant_le16_to_cpu(_Q_LOCKED_VAL) there. The > unconditional 1 is wrong. You also have to flip the bytes in > locked_pending.
I don't think that is wrong. The lock byte is in the least significant 8 bits and the pending byte is the next higher significant 8 bits irrespective of the endian-ness. So a value of 1 in a 16-bit context means the lock byte is set, but the pending byte is cleared. The name "locked_pending" doesn't mean that locked variable is in a lower address than pending.
-Longman
| |