Messages in this thread | | | Date | Tue, 20 Feb 2018 16:17:52 +0100 | From | Andrea Parri <> | Subject | Re: [PATCH] tools/memory-model: remove rb-dep, smp_read_barrier_depends, and lockless_dereference |
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On Tue, Feb 20, 2018 at 06:48:13AM -0800, Paul E. McKenney wrote: > On Mon, Feb 19, 2018 at 06:44:13PM +0100, Peter Zijlstra wrote: > > On Mon, Feb 19, 2018 at 12:14:45PM -0500, Alan Stern wrote: > > > Note that operations like atomic_add_unless() already include memory > > > barriers. > > > > It is valid for atomic_add_unless() to not imply any barriers when the > > addition doesn't happen. > > Agreed, given that atomic_add_unless() just returns 0 or 1, not the > pointer being added. Of course, the __atomic_add_unless() function > that it calls is another story, as it does return the old value. Sigh. > And __atomic_add_unless() is called directly from some code. All of > which looks to be counters rather than pointers, thankfully. > > So, do we want to rely on atomic_add_unless() always being > invoked on counters rather than pointers, or does it need an > smp_read_barrier_depends()?
alpha's implementation of __atomic_add_unless() has an unconditional smp_mb() before returning so, as far as dependencies are concerned, these seem fine.
Andrea
> > Thanx, Paul >
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