Messages in this thread | | | Date | Wed, 11 Jul 2018 17:53:55 +0200 | From | Andrea Parri <> | Subject | Re: [PATCH] doc: Replace smp_cond_acquire() with smp_cond_load_acquire() |
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On Wed, Jul 11, 2018 at 08:38:40AM -0700, Paul E. McKenney wrote: > On Wed, Jul 11, 2018 at 03:08:50PM +0200, Andrea Parri wrote: > > Amend commit 1f03e8d2919270 ("locking/barriers: Replace smp_cond_acquire() > > with smp_cond_load_acquire()") by updating the documentation accordingly. > > Also remove some obsolete information related to the implementation. > > > > Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com> > > Cc: Alan Stern <stern@rowland.harvard.edu> > > Cc: Will Deacon <will.deacon@arm.com> > > Cc: Peter Zijlstra <peterz@infradead.org> > > Cc: Boqun Feng <boqun.feng@gmail.com> > > Cc: Nicholas Piggin <npiggin@gmail.com> > > Cc: David Howells <dhowells@redhat.com> > > Cc: Jade Alglave <j.alglave@ucl.ac.uk> > > Cc: Luc Maranget <luc.maranget@inria.fr> > > Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > > Cc: Akira Yokosawa <akiyks@gmail.com> > > Cc: Daniel Lustig <dlustig@nvidia.com> > > Cc: Jonathan Corbet <corbet@lwn.net> > > --- > > Documentation/memory-barriers.txt | 3 +-- > > 1 file changed, 1 insertion(+), 2 deletions(-) > > I have queued this for further review, thank you! Just to confirm, > the reason that the old passage was obsolete is because ARMv8 implements > smp_cond_load_acquire() as a straight acquire load, correct?
Thanks. Yes; the generic code builds on a control dependency and an smp_acquire__after_ctrl_dep() (which defaults to smp_rmb()); but the required ordering on arm64 is given by (its) smp_load_acquire().
I thought that entering this level of details (and keeping it up-to- date ;) wasn't really worth/needed for this high-level doc.
Andrea
> > Thanx, Paul > > > diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt > > index 0d8d7ef131e9a..c1d913944ad8b 100644 > > --- a/Documentation/memory-barriers.txt > > +++ b/Documentation/memory-barriers.txt > > @@ -471,8 +471,7 @@ And a couple of implicit varieties: > > operations after the ACQUIRE operation will appear to happen after the > > ACQUIRE operation with respect to the other components of the system. > > ACQUIRE operations include LOCK operations and both smp_load_acquire() > > - and smp_cond_acquire() operations. The later builds the necessary ACQUIRE > > - semantics from relying on a control dependency and smp_rmb(). > > + and smp_cond_load_acquire() operations. > > > > Memory operations that occur before an ACQUIRE operation may appear to > > happen after it completes. > > -- > > 2.7.4 > > >
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