On 06/18/2014 11:32 PM, Tejun Heo wrote:
> On Wed, Jun 18, 2014 at 11:37:35AM +0800, Lai Jiangshan wrote:
>>> @@ -97,7 +98,10 @@ static inline void percpu_ref_kill(struct percpu_ref
>>> *ref)
>>> static inline bool __pcpu_ref_alive(struct percpu_ref *ref,
>>> unsigned __percpu **pcpu_countp)
>>> {
>>> - unsigned long pcpu_ptr = ACCESS_ONCE(ref->pcpu_count_ptr);
>>> + unsigned long pcpu_ptr;
>>> +
>>> + /* paired with smp_store_release() in percpu_ref_reinit() */
>>> + pcpu_ptr = smp_load_acquire(&ref->pcpu_count_ptr);
>>
>>
>> Does "smp_load_acquire()" hurts the performance of percpu_ref_get/put()
>> in non-x86 system?
>
> It's equivalent to data dependency barrier. The only arch which needs
> something more than barrier() is alpha. It isn't an issue.
>
But I searched from the source, smp_load_acquire() is just barrier() in
x86, arm64, ia64, s390, sparc, but it includes memory barrier
instruction in other archs.
CC Paul. If smp_load_acquire() is sufficient lightweight, I would update
the SRCU.
Thanks,
Lai
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