Messages in this thread | | | Date | Thu, 19 Jun 2014 09:58:16 +0800 | From | Lai Jiangshan <> | Subject | Re: [PATCH 6/6] percpu-refcount: implement percpu_ref_reinit() and percpu_ref_is_zero() |
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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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