| Message ID | 1479294769-12723-1-git-send-email-mark.rutland@arm.com |
|---|---|
| State | Accepted |
| Commit | 01e4644203b01fba5023784598f4d033e3bd3e28 |
| Headers | show |
Mark Rutland <mark.rutland@arm.com> wrote: > While the {READ,WRITE}_ONCE() macros should be used in preference to > ACCESS_ONCE(), the circular buffer documentation uses the latter > exclusively. > > To point people in the right direction, and as a step towards the > eventual removal of ACCESS_ONCE(), update the documentation to use > READ_ONCE(), as ACCESS_ONCE() is only used in a reader context in the > circular buffer documentation. > > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Cc: linux-doc@vger.kernel.org > Cc: linux-kernel@vger.kernel.org Acked-by: David Howells <dhowells@redhat.com>
On Wed, Nov 16, 2016 at 11:12:49AM +0000, Mark Rutland wrote: > While the {READ,WRITE}_ONCE() macros should be used in preference to > ACCESS_ONCE(), the circular buffer documentation uses the latter > exclusively. > > To point people in the right direction, and as a step towards the > eventual removal of ACCESS_ONCE(), update the documentation to use > READ_ONCE(), as ACCESS_ONCE() is only used in a reader context in the > circular buffer documentation. > > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Cc: David Howells <dhowells@redhat.com> > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Cc: linux-doc@vger.kernel.org > Cc: linux-kernel@vger.kernel.org Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > --- > Documentation/circular-buffers.txt | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/Documentation/circular-buffers.txt b/Documentation/circular-buffers.txt > index 88951b1..4a824d2 100644 > --- a/Documentation/circular-buffers.txt > +++ b/Documentation/circular-buffers.txt > @@ -161,7 +161,7 @@ The producer will look something like this: > > unsigned long head = buffer->head; > /* The spin_unlock() and next spin_lock() provide needed ordering. */ > - unsigned long tail = ACCESS_ONCE(buffer->tail); > + unsigned long tail = READ_ONCE(buffer->tail); > > if (CIRC_SPACE(head, tail, buffer->size) >= 1) { > /* insert one item into the buffer */ > @@ -222,7 +222,7 @@ This will instruct the CPU to make sure the index is up to date before reading > the new item, and then it shall make sure the CPU has finished reading the item > before it writes the new tail pointer, which will erase the item. > > -Note the use of ACCESS_ONCE() and smp_load_acquire() to read the > +Note the use of READ_ONCE() and smp_load_acquire() to read the > opposition index. This prevents the compiler from discarding and > reloading its cached value - which some compilers will do across > smp_read_barrier_depends(). This isn't strictly needed if you can > -- > 1.9.1 >
On Wed, 16 Nov 2016 11:12:49 +0000 Mark Rutland <mark.rutland@arm.com> wrote: > While the {READ,WRITE}_ONCE() macros should be used in preference to > ACCESS_ONCE(), the circular buffer documentation uses the latter > exclusively. > > To point people in the right direction, and as a step towards the > eventual removal of ACCESS_ONCE(), update the documentation to use > READ_ONCE(), as ACCESS_ONCE() is only used in a reader context in the > circular buffer documentation. Applied to the docs tree, thanks. jon
diff --git a/Documentation/circular-buffers.txt b/Documentation/circular-buffers.txt index 88951b1..4a824d2 100644 --- a/Documentation/circular-buffers.txt +++ b/Documentation/circular-buffers.txt @@ -161,7 +161,7 @@ The producer will look something like this: unsigned long head = buffer->head; /* The spin_unlock() and next spin_lock() provide needed ordering. */ - unsigned long tail = ACCESS_ONCE(buffer->tail); + unsigned long tail = READ_ONCE(buffer->tail); if (CIRC_SPACE(head, tail, buffer->size) >= 1) { /* insert one item into the buffer */ @@ -222,7 +222,7 @@ This will instruct the CPU to make sure the index is up to date before reading the new item, and then it shall make sure the CPU has finished reading the item before it writes the new tail pointer, which will erase the item. -Note the use of ACCESS_ONCE() and smp_load_acquire() to read the +Note the use of READ_ONCE() and smp_load_acquire() to read the opposition index. This prevents the compiler from discarding and reloading its cached value - which some compilers will do across smp_read_barrier_depends(). This isn't strictly needed if you can
While the {READ,WRITE}_ONCE() macros should be used in preference to ACCESS_ONCE(), the circular buffer documentation uses the latter exclusively. To point people in the right direction, and as a step towards the eventual removal of ACCESS_ONCE(), update the documentation to use READ_ONCE(), as ACCESS_ONCE() is only used in a reader context in the circular buffer documentation. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: David Howells <dhowells@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: linux-doc@vger.kernel.org Cc: linux-kernel@vger.kernel.org --- Documentation/circular-buffers.txt | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) -- 1.9.1