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

[Peter Zijlstra]

On Tue, Aug 27, 2013 at 06:21:29PM -0700, Paul E. McKenney wrote:
> On Tue, Aug 27, 2013 at 03:53:10PM +0200, Peter Zijlstra wrote:
> > 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.
> 
> An unlock followed by a lock needs to act like a full barrier, but there
> is no requirement that a lock or unlock taken separately act like a
> full barrier.

But that is already a property of the acquisition/release barrier.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/