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Re: questions about memory_order_seq_cst fence

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From Alexander Terekhov <terekhov@web.de>
Newsgroups comp.programming.threads
Subject Re: questions about memory_order_seq_cst fence
Date Thu, 16 Jun 2011 17:25:58 +0200
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Addition re "Incorrect implementation" below:

Alexander Terekhov wrote:
> 
> Anthony Williams wrote:
> [...]
> > LOCKed instructions have a total order (7.2.3.8 in my copy of the Intel
> > 64 and IA-32 SDM Vol 3A), so if you use XCHG for stores (as per my blog
> > post) then all processors/threads must agree on the order of the writes.
> >
> > This is the key to SC --- all SC stores must have a single total order
> > which is agreed across all threads.
> >
> > Why do you think this is not enough?
> 
> In
> 
>   x.store(44, memory_order_relaxed); // or _release
>   r1 = y.load(memory_order_seq_cst);
> 
> there should be a store-load reordering constraint, just like in
> 
>   x.store(44, memory_order_seq_cst);
>   r1 = y.load(memory_order_relaxed); // or _acquire/_consume
> 
> Implementation 1:
> 
>   Load Seq_Cst:  LOCK XADD(0)
>   Store Seq_Cst: LOCK XCHG
> 
> Implementation 2:
> 
>   Load Seq_Cst:  LOCK XADD(0)
>   Store Seq_Cst: MOV, MFENCE
> 
> Implementation 3:
> 
>   Load Seq_Cst:  MFENCE, MOV
>   Store Seq_Cst: LOCK XCHG
> 
> Incorrect implementation
> 
>   Load Seq_Cst:  MFENCE, MOV
>   Store Seq_Cst: MOV, MFENCE
> 
> is busted because IRIW won't work.

That is my thinking... but according to 

http://portal.acm.org/citation.cfm?id=1926394

the "Incorrect implementation" above is actually correct (probably
because according to them, MFENCE has the same semantics as PPC's
hwsync).

(I'm personally still in doubt).

regards,
alexander.

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Thread

questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-13 09:40 -0700
  Re: questions about memory_order_seq_cst fence Edek <edek.pienkowski@gmail.com> - 2011-06-13 22:39 +0200
    Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-14 08:27 -0700
      Re: questions about memory_order_seq_cst fence Edek <edek.pienkowski@gmail.com> - 2011-06-16 00:21 +0200
        Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-15 15:48 -0700
          Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-16 05:03 -0700
        Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 08:35 +0100
          Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 12:05 +0200
            Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 11:19 +0100
              Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 13:57 +0200
                Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 13:51 +0100
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 16:53 +0200
                Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 16:17 +0100
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 17:37 +0200
                Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-16 08:47 -0700
                Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 16:54 +0100
                Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-16 09:01 -0700
                Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 17:07 +0100
                Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-16 13:59 -0700
                Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-16 14:32 -0700
                Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-17 08:03 +0100
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-17 16:19 +0200
                Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-17 15:40 +0100
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-30 14:26 +0200
                Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-17 15:24 -0700
                Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-18 03:49 -0700
                Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-18 14:40 -0700
                Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-18 15:46 -0700
                Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-18 20:27 -0700
                Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-18 21:31 -0700
                Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-18 21:37 -0700
                Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-20 15:45 -0700
                Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-20 20:05 -0700
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-18 14:06 +0200
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 18:32 +0200
                Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-16 15:42 -0700
                Re: questions about memory_order_seq_cst fence Edek <edek.pienkowski@gmail.com> - 2011-07-10 19:47 +0200
                Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-16 08:51 -0700
                Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 17:23 +0100
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 18:49 +0200
                Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-16 08:51 -0700
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 17:25 +0200
                Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 16:56 +0100
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-18 14:28 +0200
                Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-20 09:54 +0100
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-20 15:39 +0200
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-22 13:24 +0200
          Re: questions about memory_order_seq_cst fence Edek <edek.pienkowski@gmail.com> - 2011-06-16 14:39 +0200
            Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 13:55 +0100
        Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-16 12:03 +0200
          Re: questions about memory_order_seq_cst fence Edek <edek.pienkowski@gmail.com> - 2011-07-10 19:10 +0200
  Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-13 16:00 -0700
    Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-13 23:31 -0700
      Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-14 08:32 -0700
  Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-14 23:05 +0100
    Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-14 16:44 -0700
      Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-15 08:34 +0100
        Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-15 02:11 -0700
        Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-15 15:58 -0700
        Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 08:26 +0100
          Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-16 05:05 -0700
            Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-16 13:11 +0100
              Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-18 15:42 +0200
                Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-20 09:27 +0100
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-20 15:30 +0200
                Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-20 15:00 +0100
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-21 14:54 +0200
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-21 18:37 +0200
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-21 15:59 +0200
                Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-22 09:01 -0700
                Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-20 15:41 +0100
                Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-20 23:24 -0700
                Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-22 10:46 -0700
                Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-22 11:19 -0700
                Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-22 11:57 -0700
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-27 14:05 +0200
                Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-29 16:14 -0700
                Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-06-24 01:42 -0700
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-06-27 13:24 +0200
                Re: questions about memory_order_seq_cst fence Anthony Williams <anthony.ajw@gmail.com> - 2011-07-01 02:25 -0700
                Re: questions about memory_order_seq_cst fence Alexander Terekhov <terekhov@web.de> - 2011-07-01 12:48 +0200
      Re: questions about memory_order_seq_cst fence Masakuni Oishi <yamasa@bsdhouse.org> - 2011-06-15 01:53 -0700
        Re: questions about memory_order_seq_cst fence Joshua Maurice <joshuamaurice@gmail.com> - 2011-06-15 02:57 -0700
    Re: questions about memory_order_seq_cst fence "Chris M. Thomasson" <cristom@charter.net> - 2011-06-15 02:06 -0700

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