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Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

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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

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[PATCH tip/core/rcu 0/14] Documentation updates for 4.6 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 01/14] documentation:  Add real-time requirements from CPU-bound workloads "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 14/14] documentation: Clarify compiler store-fusion example "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 12/14] documentation: Document illegality of call_rcu() from offline CPUs "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 07/14] documentation: Distinguish between local and global transitivity "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 05/14] documentation: Remove obsolete reference to RCU-protected indexes "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 08/14] documentation:  Add alternative release-acquire outcome "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 11/14] documentation: Transitivity is not cumulativity "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 04/14] documentation: Add synchronize_rcu_mult() to the requirements "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 13/14] documentation: Explain how RCU's combining tree fights contention "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100
  [PATCH tip/core/rcu 10/14] documentation: Explain why rcu_read_lock() needs no barrier() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100
  [PATCH tip/core/rcu 03/14] documentation: Fix memory-barriers.txt section references "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100
  [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100
    Re: [PATCH tip/core/rcu 02/14] documentation: Fix control  dependency and identical stores Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-02-24 22:20 +0100
      Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency  and identical stores "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 22:50 +0100
        Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency  and identical stores Jianyu Zhan <nasa4836@gmail.com> - 2016-02-25 07:50 +0100
          Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency  and identical stores "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-25 15:10 +0100
        Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency  and identical stores Peter Zijlstra <peterz@infradead.org> - 2016-02-25 09:30 +0100
          Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency  and identical stores "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-25 15:10 +0100
            Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency  and identical stores Peter Zijlstra <peterz@infradead.org> - 2016-02-25 15:50 +0100
              Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency  and identical stores "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-25 16:50 +0100
  [PATCH tip/core/rcu 06/14] documentation: Subsequent writes ordered by rcu_dereference() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100

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