summaryrefslogtreecommitdiffstats
path: root/Documentation/memory-barriers.txt
diff options
context:
space:
mode:
authorPeter Zijlstra <peterz@infradead.org>2014-03-13 19:00:35 +0100
committerIngo Molnar <mingo@kernel.org>2014-04-18 14:20:48 +0200
commit1b15611e1c30b37abe393d411c316cd659920bf5 (patch)
tree99992be63b630b8a64135f47e2f93f90db7cbab1 /Documentation/memory-barriers.txt
parent09a01c0ccb1837abb28afcfdd668fa0dfabed928 (diff)
downloadop-kernel-dev-1b15611e1c30b37abe393d411c316cd659920bf5.zip
op-kernel-dev-1b15611e1c30b37abe393d411c316cd659920bf5.tar.gz
arch,doc: Convert smp_mb__*()
Update the documentation to reflect the change of barrier primitives. Signed-off-by: Peter Zijlstra <peterz@infradead.org> Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: David Howells <dhowells@redhat.com> Link: http://lkml.kernel.org/n/tip-xslfehiga1twbk5uk94rij1e@git.kernel.org Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: linux-doc@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'Documentation/memory-barriers.txt')
-rw-r--r--Documentation/memory-barriers.txt42
1 files changed, 11 insertions, 31 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index 556f951..46412bd 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1583,20 +1583,21 @@ There are some more advanced barrier functions:
insert anything more than a compiler barrier in a UP compilation.
- (*) smp_mb__before_atomic_dec();
- (*) smp_mb__after_atomic_dec();
- (*) smp_mb__before_atomic_inc();
- (*) smp_mb__after_atomic_inc();
+ (*) smp_mb__before_atomic();
+ (*) smp_mb__after_atomic();
- These are for use with atomic add, subtract, increment and decrement
- functions that don't return a value, especially when used for reference
- counting. These functions do not imply memory barriers.
+ These are for use with atomic (such as add, subtract, increment and
+ decrement) functions that don't return a value, especially when used for
+ reference counting. These functions do not imply memory barriers.
+
+ These are also used for atomic bitop functions that do not return a
+ value (such as set_bit and clear_bit).
As an example, consider a piece of code that marks an object as being dead
and then decrements the object's reference count:
obj->dead = 1;
- smp_mb__before_atomic_dec();
+ smp_mb__before_atomic();
atomic_dec(&obj->ref_count);
This makes sure that the death mark on the object is perceived to be set
@@ -1606,27 +1607,6 @@ There are some more advanced barrier functions:
operations" subsection for information on where to use these.
- (*) smp_mb__before_clear_bit(void);
- (*) smp_mb__after_clear_bit(void);
-
- These are for use similar to the atomic inc/dec barriers. These are
- typically used for bitwise unlocking operations, so care must be taken as
- there are no implicit memory barriers here either.
-
- Consider implementing an unlock operation of some nature by clearing a
- locking bit. The clear_bit() would then need to be barriered like this:
-
- smp_mb__before_clear_bit();
- clear_bit( ... );
-
- This prevents memory operations before the clear leaking to after it. See
- the subsection on "Locking Functions" with reference to RELEASE operation
- implications.
-
- See Documentation/atomic_ops.txt for more information. See the "Atomic
- operations" subsection for information on where to use these.
-
-
MMIO WRITE BARRIER
------------------
@@ -2283,11 +2263,11 @@ operations:
change_bit();
With these the appropriate explicit memory barrier should be used if necessary
-(smp_mb__before_clear_bit() for instance).
+(smp_mb__before_atomic() for instance).
The following also do _not_ imply memory barriers, and so may require explicit
-memory barriers under some circumstances (smp_mb__before_atomic_dec() for
+memory barriers under some circumstances (smp_mb__before_atomic() for
instance):
atomic_add();
OpenPOWER on IntegriCloud