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

[Andi Kleen]

> 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

-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only.
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