From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de,
peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com,
edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com,
oleg@redhat.com, sbw@mit.edu,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 3/6] Documentation/memory-barriers.txt: Conditional must use prior load
Date: Mon, 17 Feb 2014 13:26:50 -0800 [thread overview]
Message-ID: <1392672413-5114-3-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <1392672413-5114-1-git-send-email-paulmck@linux.vnet.ibm.com>
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
A control dependency consists of a load, a conditional that depends on
that load, and a store. This commit emphasizes this point in the
summary.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
Documentation/memory-barriers.txt | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index ad6db1d48f1f..f2668c19807e 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -724,7 +724,8 @@ In summary:
later loads, smp_mb().
(*) Control dependencies require at least one run-time conditional
- between the prior load and the subsequent store. If the compiler
+ between the prior load and the subsequent store, and this
+ conditional must involve the prior load. If the compiler
is able to optimize the conditional away, it will have also
optimized away the ordering. Careful use of ACCESS_ONCE() can
help to preserve the needed conditional.
--
1.8.1.5
next prev parent reply other threads:[~2014-02-17 21:28 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-17 21:26 [PATCH tip/core/rcu 0/6] Documentation changes for 3.15 Paul E. McKenney
2014-02-17 21:26 ` [PATCH tip/core/rcu 1/6] documentation: Document call_rcu() safety mechanisms and limitations Paul E. McKenney
2014-02-17 21:26 ` [PATCH tip/core/rcu 2/6] Documentation/memory-barriers.txt: ACCESS_ONCE() provides cache coherence Paul E. McKenney
2014-02-17 21:40 ` Josh Triplett
2014-02-17 22:52 ` Paul E. McKenney
2014-02-17 21:26 ` Paul E. McKenney [this message]
2014-02-17 21:26 ` [PATCH tip/core/rcu 4/6] Documentation/kernel-per-CPU-kthreads.txt: Workqueue affinity Paul E. McKenney
2014-02-17 21:26 ` [PATCH tip/core/rcu 5/6] Documentation/memory-barriers.txt: Need barriers() for some control dependencies Paul E. McKenney
2014-02-17 21:46 ` Josh Triplett
2014-02-17 22:58 ` Paul E. McKenney
2014-02-18 0:02 ` Josh Triplett
2014-02-18 0:17 ` Paul E. McKenney
2014-02-18 0:45 ` Josh Triplett
2014-02-18 1:21 ` Paul E. McKenney
2014-02-18 3:29 ` Josh Triplett
2014-02-18 4:57 ` Paul E. McKenney
2014-02-17 21:26 ` [PATCH tip/core/rcu 6/6] documentation: Fix some inconsistencies in RTFP.txt Paul E. McKenney
2014-02-17 21:39 ` [PATCH tip/core/rcu 1/6] documentation: Document call_rcu() safety mechanisms and limitations Josh Triplett
2014-02-17 22:52 ` Paul E. McKenney
2014-02-17 21:47 ` [PATCH tip/core/rcu 0/6] Documentation changes for 3.15 Josh Triplett
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