[PATCH] doc: Replace smp_cond_acquire() with smp_cond_load_acquire()

[PATCH] doc: Replace smp_cond_acquire() with smp_cond_load_acquire()

[Andrea Parri]

Amend commit 1f03e8d2919270 ("locking/barriers: Replace smp_cond_acquire()
with smp_cond_load_acquire()") by updating the documentation accordingly.

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 | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index 0d8d7ef131e9a..987a4e6cc0cd8 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -471,8 +471,8 @@ 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. The later builds the necessary
+     ACQUIRE semantics from relying on a control dependency and smp_rmb().
 
      Memory operations that occur before an ACQUIRE operation may appear to
      happen after it completes.
-- 
2.7.4

Re: [PATCH] doc: Replace smp_cond_acquire() with smp_cond_load_acquire()

[Andrea Parri]

On Tue, Jul 10, 2018 at 12:02:23PM +0200, Andrea Parri wrote:
> Amend commit 1f03e8d2919270 ("locking/barriers: Replace smp_cond_acquire()
> with smp_cond_load_acquire()") by updating the documentation accordingly.
> 
> 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 | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
> index 0d8d7ef131e9a..987a4e6cc0cd8 100644
> --- a/Documentation/memory-barriers.txt
> +++ b/Documentation/memory-barriers.txt
> @@ -471,8 +471,8 @@ 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. The later builds the necessary
> +     ACQUIRE semantics from relying on a control dependency and smp_rmb().

Still not completely accurate: smp_rmb() would better be replaced by
smp_acquire__after_ctrl_dep() (arm64 excluded).  Mmh... I think I'll
just remove that "The latter builds the [...]" and resend; thoughts?

  Andrea


>  
>       Memory operations that occur before an ACQUIRE operation may appear to
>       happen after it completes.
> -- 
> 2.7.4
> 

[PATCH] doc: Replace smp_cond_acquire() with smp_cond_load_acquire()

[Andrea Parri]

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(-)

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

Re: [PATCH] doc: Replace smp_cond_acquire() with smp_cond_load_acquire()

[Paul E. McKenney]

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?

							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
> 

Re: [PATCH] doc: Replace smp_cond_acquire() with smp_cond_load_acquire()

[Andrea Parri]

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
> > 
> 

Re: [PATCH] doc: Replace smp_cond_acquire() with smp_cond_load_acquire()

[Paul E. McKenney]

On Wed, Jul 11, 2018 at 05:53:55PM +0200, Andrea Parri wrote:
> 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.

Agreed!

							Thanx, Paul

>   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
> > > 
> > 
>