Re: [PATCH RFC v2 1/2] qspinlock: Introducing a 4-byte queuespinlock implementation

[Peter Zijlstra]

On Tue, Aug 27, 2013 at 09:14:36AM -0400, Steven Rostedt wrote:

> I just had this conversation with Paul McKenney. Should there be a
> smp_mb_after_spin_unlock()?

Depends on the benefits I suppose :-) Oleg and Linus did recently add
smp_mb__before_spinlock();

> Although we blew it off as adding too many extensions to smp_mb(). But
> it may be better than reimplementing something as complex as a lock.

Locks should be as light weight as possible and never implement anything
heavier than the ACQUISITION / RELEASE barriers if at all possible. We
should certainly not re-implement spinlocks just to get full barriers
out of them, that's crazy.
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