Commit-ID: b26cfc48e3e03126c183f1f3960e6d69460bb852
Gitweb: http://git.kernel.org/tip/b26cfc48e3e03126c183f1f3960e6d69460bb852
Author: pierre Kuo <vichy.kuo@xxxxxxxxx>
AuthorDate: Fri, 7 Apr 2017 14:37:36 +0800
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Wed, 12 Apr 2017 08:23:43 -0700
doc: Update control-dependencies section of memory-barriers.txt
In the following example, if MAX is defined to be 1, then the compiler
knows (Q % MAX) is equal to zero. The compiler can therefore throw
away the "then" branch (and the "if"), retaining only the "else" branch.
q = READ_ONCE(a);
if (q % MAX) {
WRITE_ONCE(b, 1);
do_something();
} else {
WRITE_ONCE(b, 2);
do_something_else();
}
It is therefore necessary to modify the example like this:
q = READ_ONCE(a);
- WRITE_ONCE(b, 1);
+ WRITE_ONCE(b, 2);
do_something_else();
Signed-off-by: pierre Kuo <vichy.kuo@xxxxxxxxx>
Acked-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
Documentation/memory-barriers.txt | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index d2b0a8d..08329cb 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -768,7 +768,7 @@ equal to zero, in which case the compiler is within its rights to
transform the above code into the following:
q = READ_ONCE(a);
- WRITE_ONCE(b, 1);
+ WRITE_ONCE(b, 2);
do_something_else();
Given this transformation, the CPU is not required to respect the ordering
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