From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Jianyu Zhan <nasa4836@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
dipankar@in.ibm.com, Andrew Morton <akpm@linux-foundation.org>,
josh@joshtriplett.org, Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
rostedt <rostedt@goodmis.org>,
David Howells <dhowells@redhat.com>,
Eric Dumazet <edumazet@google.com>,
dvhart@linux.intel.com, fweisbec@gmail.com,
Oleg Nesterov <oleg@redhat.com>,
bobby prani <bobby.prani@gmail.com>
Subject: Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores
Date: Thu, 25 Feb 2016 06:08:16 -0800 [thread overview]
Message-ID: <20160225140816.GK3522@linux.vnet.ibm.com> (raw)
In-Reply-To: <CAHz2CGVSJDdTKkBfoczd51A6+xQML5RzVc2BmbRBgoNntXXmyg@mail.gmail.com>
On Thu, Feb 25, 2016 at 02:41:07PM +0800, Jianyu Zhan wrote:
> On Thu, Feb 25, 2016 at 5:40 AM, Paul E. McKenney
> <paulmck@linux.vnet.ibm.com> wrote:
> > So ordering between the read from "a" and the write to "b" is still
> > preserved. The reason this works is that the smp_mb() does all the
> > ordering, so the fact that the control dependency has been eliminated
> > is irrelevant.
>
>
> Thanks, Paul, nice clarification.
>
> I thinks this example qualifies as an good example to demonstrate the subtle
> scope of effect of these two level barriers.
>
> A vivid example is always better for understanding instead of learning
> "barrier() is compiler-level
> barrier, and smp_*mb() is processor-level barrier" by rote ,
> especially for the new comers to memory-barriers.txt. ;-)
Glad you like it. ;-)
Thanx, Paul
next prev parent reply other threads:[~2016-02-25 14:08 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-24 5:00 [PATCH tip/core/rcu 0/14] Documentation updates for 4.6 Paul E. McKenney
2016-02-24 5:00 ` [PATCH tip/core/rcu 01/14] documentation: Add real-time requirements from CPU-bound workloads Paul E. McKenney
2016-02-24 5:00 ` [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores Paul E. McKenney
2016-02-24 21:12 ` Mathieu Desnoyers
2016-02-24 21:40 ` Paul E. McKenney
2016-02-25 6:41 ` Jianyu Zhan
2016-02-25 14:08 ` Paul E. McKenney [this message]
2016-02-25 8:21 ` Peter Zijlstra
2016-02-25 14:07 ` Paul E. McKenney
2016-02-25 14:48 ` Peter Zijlstra
2016-02-25 15:42 ` Paul E. McKenney
2016-02-24 5:00 ` [PATCH tip/core/rcu 03/14] documentation: Fix memory-barriers.txt section references Paul E. McKenney
2016-02-24 5:00 ` [PATCH tip/core/rcu 04/14] documentation: Add synchronize_rcu_mult() to the requirements Paul E. McKenney
2016-02-24 5:00 ` [PATCH tip/core/rcu 05/14] documentation: Remove obsolete reference to RCU-protected indexes Paul E. McKenney
2016-02-24 5:00 ` [PATCH tip/core/rcu 06/14] documentation: Subsequent writes ordered by rcu_dereference() Paul E. McKenney
2016-02-24 5:00 ` [PATCH tip/core/rcu 07/14] documentation: Distinguish between local and global transitivity Paul E. McKenney
2016-02-24 5:00 ` [PATCH tip/core/rcu 08/14] documentation: Add alternative release-acquire outcome Paul E. McKenney
2016-02-24 5:00 ` [PATCH tip/core/rcu 09/14] documentation: Add documentation for RCU's major data structures Paul E. McKenney
2016-02-24 5:00 ` [PATCH tip/core/rcu 10/14] documentation: Explain why rcu_read_lock() needs no barrier() Paul E. McKenney
2016-02-24 5:00 ` [PATCH tip/core/rcu 11/14] documentation: Transitivity is not cumulativity Paul E. McKenney
2016-02-24 5:00 ` [PATCH tip/core/rcu 12/14] documentation: Document illegality of call_rcu() from offline CPUs Paul E. McKenney
2016-02-24 5:00 ` [PATCH tip/core/rcu 13/14] documentation: Explain how RCU's combining tree fights contention Paul E. McKenney
2016-02-24 5:00 ` [PATCH tip/core/rcu 14/14] documentation: Clarify compiler store-fusion example Paul E. McKenney
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=20160225140816.GK3522@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=nasa4836@gmail.com \
--cc=oleg@redhat.com \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
/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