Commit-ID: 128ea442b12ba63614dccc9b54726cf753aa4758 Gitweb: http://git.kernel.org/tip/128ea442b12ba63614dccc9b54726cf753aa4758 Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> AuthorDate: Thu, 19 Jun 2014 10:01:23 -0700 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Tue, 8 Jul 2014 08:32:51 -0700 documentation: Add acquire/release barriers to pairing rules It is possible to pair acquire and release barriers with other barriers, so this commit adds them to the list in the SMP barrier pairing section. Reported-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> Reviewed-by: Tejun Heo <tj@xxxxxxxxxx> Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx> [ paulmck: Updated pairing discussion as suggested by Peter Zijlstra. ] --- Documentation/memory-barriers.txt | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index a6ca533..a4de88f 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -757,10 +757,14 @@ SMP BARRIER PAIRING When dealing with CPU-CPU interactions, certain types of memory barrier should always be paired. A lack of appropriate pairing is almost certainly an error. -A write barrier should always be paired with a data dependency barrier or read -barrier, though a general barrier would also be viable. Similarly a read -barrier or a data dependency barrier should always be paired with at least an -write barrier, though, again, a general barrier is viable: +General barriers pair with each other, though they also pair with +most other types of barriers, albeit without transitivity. An acquire +barrier pairs with a release barrier, but both may also pair with other +barriers, including of course general barriers. A write barrier pairs +with a data dependency barrier, an acquire barrier, a release barrier, +a read barrier, or a general barrier. Similarly a read barrier or a +data dependency barrier pairs with a write barrier, an acquire barrier, +a release barrier, or a general barrier: CPU 1 CPU 2 =============== =============== -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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