lkml.org 
[lkml]   [2014]   [Apr]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [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


\
 
 \ /
  Last update: 2014-04-18 00:21    [W:0.103 / U:0.204 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site