Re: [PATCH v8 14/19] locking/rwsem: Enable time-based spinning on reader-owned rwsem

From: Waiman Long
Date: Tue Jun 04 2019 - 12:58:44 EST


On 6/4/19 5:03 AM, Peter Zijlstra wrote:
> On Mon, May 20, 2019 at 04:59:13PM -0400, Waiman Long wrote:
>> +static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
>> +{
>> + long owner = atomic_long_read(&sem->owner);
>> +
>> + while (owner & RWSEM_READER_OWNED) {
>> + if (owner & RWSEM_NONSPINNABLE)
>> + break;
>> + owner = atomic_long_cmpxchg(&sem->owner, owner,
>> + owner | RWSEM_NONSPINNABLE);
>> + }
>> +}
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -206,12 +206,13 @@ static inline void rwsem_set_nonspinnabl
> {
> long owner = atomic_long_read(&sem->owner);
>
> - while (owner & RWSEM_READER_OWNED) {
> + do {
> + if (!(owner & RWSEM_READER_OWNED))
> + break;
> if (owner & RWSEM_NONSPINNABLE)
> break;
> - owner = atomic_long_cmpxchg(&sem->owner, owner,
> - owner | RWSEM_NONSPINNABLE);
> - }
> + } while (!atomic_long_try_cmpxchg(&sem->owner, &owner,
> + owner | RWSEM_NONSPINNABLE));
> }
>
> /*

Sure.

Thanks,
Longman