Re: [Xen-devel] [v3,11/41] mips: reuse asm-generic/barrier.h

["Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>]

On Fri, Jan 15, 2016 at 10:29:12PM +0100, Peter Zijlstra wrote:
> On Fri, Jan 15, 2016 at 09:39:12AM -0800, Paul E. McKenney wrote:
> > Should we start putting litmus tests for the various examples
> > somewhere, perhaps in a litmus-tests directory within each participating
> > architecture?  I have a pile of powerpc-related litmus tests on my laptop,
> > but they probably aren't doing all that much good there.
> 
> Yeah, or a version of them in C that we can 'compile'?

That would be good as well.  I am guessing that architecture-specific
litmus tests will also be needed, but you are right that
architecture-independent versions are higher priority.

> > commit 2cb4e83a1b5c89c8e39b8a64bd89269d05913e41
> > Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> > Date:   Fri Jan 15 09:30:42 2016 -0800
> > 
> >     documentation: Distinguish between local and global transitivity
> >     
> >     The introduction of smp_load_acquire() and smp_store_release() had
> >     the side effect of introducing a weaker notion of transitivity:
> >     The transitivity of full smp_mb() barriers is global, but that
> >     of smp_store_release()/smp_load_acquire() chains is local.  This
> >     commit therefore introduces the notion of local transitivity and
> >     gives an example.
> >     
> >     Reported-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> >     Reported-by: Will Deacon <will.deacon@xxxxxxx>
> >     Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> 
> I think it fails to mention smp_mb__after_release_acquire(), although I
> suspect we didn't actually introduce the primitive yet, which raises the
> point, do we want to?

Well, it is not in v4.4.  I believe that we need good use cases before
we add it.

                                                        Thanx, Paul


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