Re: [PATCH v2 1/2] spinlock: New spinlock_refcount.h for locklessupdate of refcount

[Waiman Long]

On 06/26/2013 09:06 PM, Andi Kleen wrote:
> > In the uncontended case, doing spin_unlock_wait will be similar to
> > spin_can_lock. This, when combined with a cmpxchg, is still faster
> > than doing 2 atomic operations in spin_lock/spin_unlock.
> I'm totally against any new users of spin_unlock_wait()
>
> It has bizarre semantics, most likely will make various
> lock optimizations impossible, it's race condition hell
> for most users etc.
>
> spin_can_lock() is not quite as bad has a lot of the similar problems.
>
> > BTW, spin_can_lock is just the negation of spin_is_locked.
> e.g. with elision it's not.
>
> -Andi

OK, it is about Haswell's lock elision feature. I will see what I can do 
to remove those problematic function calls.

Regards,
Longman
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