Re: [PATCH] Documentation: atomic_t.txt: Explain ordering provided by smp_mb__{before,after}_atomic()

[Paul E. McKenney]

On Tue, Apr 23, 2019 at 03:26:20PM +0200, Peter Zijlstra wrote:
> On Tue, Apr 23, 2019 at 06:21:16AM -0700, Paul E. McKenney wrote:
> > On Tue, Apr 23, 2019 at 02:17:15PM +0200, Peter Zijlstra wrote:
> > > On Sat, Apr 20, 2019 at 01:54:40AM -0700, Paul E. McKenney wrote:
> > > > 3.	Make non-value-returning atomics provide full ordering.
> > > > 	This would of course need some benchmarking, but would be a
> > > > 	simple change to make and would eliminate a large class of
> > > > 	potential bugs.  My guess is that the loss in performance
> > > > 	would be non-negligible, but who knows?
> > > 
> > > Well, only for the architectures that have
> > > smp_mb__{before,after}_atomic() as barrier(), which are: ia64, mips,
> > > s390, sparc, x86 and xtense.
> > 
> > The weakly ordered architectures would need to add the equivalent of
> > smp_mb() before and after, right?  This might result in a more noticeable
> > loss of performance.
> 
> The weak archs already have: smp_mb__{before,after}_atomic() :=
> smp_mb().

Agreed, but I thought that one of the ideas going forward was to get
rid of smp_mb__{before,after}_atomic().

							Thanx, Paul