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doc: Fix memory-barrier control-dependency example 

Each control-dependency example needs its barriers between the "if"
condition and the body of the "if" because a control dependency is
a dependency induced by a branch.  This commit makes the needed
adjustment.

Reported-by: Yongming Shen <symingz@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
hifive-unleashed-5.1
Paul E. McKenney 2013-07-02 15:24:09 -07:00
parent 6ae3771850
commit 45c8a36a55
1 changed files with 6 additions and 4 deletions
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10
Documentation/memory-barriers.txt
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@ -531,9 +531,10 @@ dependency barrier to make it work correctly. Consider the following bit of
code:
q = &a;
if (p)
if (p) {
<data dependency barrier>
q = &b;
<data dependency barrier>
}
x = *q;
This will not have the desired effect because there is no actual data
@ -542,9 +543,10 @@ attempting to predict the outcome in advance. In such a case what's actually
required is:
q = &a;
if (p)
if (p) {
<read barrier>
q = &b;
<read barrier>
}
x = *q;