From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com,
bobby.prani@gmail.com, pierre Kuo <vichy.kuo@gmail.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 9/9] doc: Update control-dependencies section of memory-barriers.txt
Date: Wed, 12 Apr 2017 09:40:22 -0700 [thread overview]
Message-ID: <1492015222-16373-9-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <20170412163956.GA15691@linux.vnet.ibm.com>
From: pierre Kuo <vichy.kuo@gmail.com>
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@gmail.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
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 d2b0a8d81258..08329cb857ed 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
--
2.5.2
prev parent reply other threads:[~2017-04-12 16:41 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-12 16:39 [PATCH tip/core/rcu 0/9] Documentation updates for 4.12 Paul E. McKenney
2017-04-12 16:40 ` [PATCH tip/core/rcu 1/9] doc: Synchronous RCU grace periods are now legal throughout boot Paul E. McKenney
2017-04-13 9:07 ` Peter Zijlstra
2017-04-13 15:56 ` Paul E. McKenney
2017-04-12 16:40 ` [PATCH tip/core/rcu 2/9] doc: Add mid-boot operation to expedited grace periods Paul E. McKenney
2017-04-12 16:40 ` [PATCH tip/core/rcu 3/9] doc: Update stallwarn.txt to make causes more prominent Paul E. McKenney
2017-04-12 16:40 ` [PATCH tip/core/rcu 4/9] doc: Update RCU data-structure documentation for rcu_segcblist Paul E. McKenney
2017-04-12 16:40 ` [PATCH tip/core/rcu 5/9] doc: Update requirements based on recent changes Paul E. McKenney
2017-04-12 16:40 ` [PATCH tip/core/rcu 6/9] doc: Update rcu_assign_pointer() definition in whatisRCU.txt Paul E. McKenney
2017-04-12 16:40 ` [PATCH tip/core/rcu 7/9] doc: Update the comparisons rule in rcu_dereference.txt Paul E. McKenney
2017-04-12 16:40 ` [PATCH tip/core/rcu 8/9] doc: Emphasize that "toy" RCU requires recursive rwlock Paul E. McKenney
2017-04-12 16:40 ` Paul E. McKenney [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1492015222-16373-9-git-send-email-paulmck@linux.vnet.ibm.com \
--to=paulmck@linux.vnet.ibm.com \
--cc=akpm@linux-foundation.org \
--cc=bobby.prani@gmail.com \
--cc=dhowells@redhat.com \
--cc=dipankar@in.ibm.com \
--cc=dvhart@linux.intel.com \
--cc=edumazet@google.com \
--cc=fweisbec@gmail.com \
--cc=jiangshanlai@gmail.com \
--cc=josh@joshtriplett.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mingo@kernel.org \
--cc=oleg@redhat.com \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
--cc=vichy.kuo@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).