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Re: big-little

From Andrew Reilly <areilly---@bigpond.net.au>
Newsgroups comp.arch
Subject Re: big-little
Date 2011-10-26 11:45 +0000
Message-ID <9gqa79FkhcU1@mid.individual.net> (permalink)
References <j7pu4q$ndv$1@USTR-NEWS.TR.UNISYS.COM> <j86o2i$83b$1@gosset.csi.cam.ac.uk> <4EA774C4.4040505@SPAM.comp-arch.net> <072ln8-su1.ln1@ntp6.tmsw.no> <j88kqj$duk$1@gosset.csi.cam.ac.uk>

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On Wed, 26 Oct 2011 10:44:51 +0100, nmm1 wrote:

> In article <072ln8-su1.ln1@ntp6.tmsw.no>,
> Terje Mathisen  <"terje.mathisen at tmsw.no"> wrote:

>>Every process observing/using/updating any item will either get the
>>previous value, or the updated value, and never something that's
>>half-way updated.
> 
> Yes, but that's not enough!

Not enough for what?  I admit to not being particularly down with the 
modern computer science, but I've done some multi-processor code.  That 
sounds like about as much consistency as one could hope for, in general.

>  Dekker's algorithm and others can fail even
> if that is true.  Consider this example:
> 
>         Thread 1        Thread 2
>                Synchronise
>           A = 1           B = 1
>          Print B         Print A
> 
> On Intel and AMD systems, you can and do have both print statements
> print zero.  The writes are atomic but not sequentially consistent.

Sure they are.  Imagine that thread 1 and thread 2 are far away from each 
other.  Why should either see modifications that originate at the other 
before they go on and do something else?  Each thread is perfectly 
consistent with it's own view of the world, which is all that it has.

> See Litmus in:
> 
>     http://www.cl.cam.ac.uk/~pes20/weakmemory/index.html

Thanks for that link.  I haven't read it (and the linked pages) yet, but 
it looks quite comprehensive.

I'm just posting because I'm curious.  What real algorithms and 
applications care or break as a result of the situation you described in 
your example?

Cheers,

-- 
Andrew

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big-little timcaffrey@aol.com (Tim McCaffrey) - 2011-10-20 19:51 +0000
  Re: big-little Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-20 22:35 +0200
    Re: big-little Mark Thorson <nospam@sonic.net> - 2011-10-20 14:18 -0800
      Re: big-little nmm1@cam.ac.uk - 2011-10-21 07:54 +0100
        Re: big-little David Kanter <dkanter@gmail.com> - 2011-11-09 01:06 -0800
          Re: big-little nmm1@cam.ac.uk - 2011-11-09 11:07 +0000
      Re: big-little Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-21 09:25 +0200
      Re: big-little EricP <ThatWouldBeTelling@thevillage.com> - 2011-10-21 11:07 -0400
        Re: big-little timcaffrey@aol.com (Tim McCaffrey) - 2011-10-21 16:28 +0000
          Re: big-little nmm1@cam.ac.uk - 2011-10-21 17:07 +0100
          Re: big-little EricP <ThatWouldBeTelling@thevillage.com> - 2011-10-21 13:25 -0400
            Re: big-little timcaffrey@aol.com (Tim McCaffrey) - 2011-10-21 19:45 +0000
              Re: big-little EricP <ThatWouldBeTelling@thevillage.com> - 2011-10-22 14:44 -0400
          Re: big-little ChrisQ <meru@devnull.com> - 2011-10-22 16:57 +0000
            Re: big-little nmm1@cam.ac.uk - 2011-10-22 17:40 +0100
              Re: big-little ChrisQ <meru@devnull.com> - 2011-10-23 14:39 +0000
                Re: big-little nmm1@cam.ac.uk - 2011-10-23 16:11 +0100
                Re: big-little ChrisQ <meru@devnull.com> - 2011-10-23 17:44 +0000
                Re: big-little nmm1@cam.ac.uk - 2011-10-23 18:46 +0100
                Re: big-little Thomas Womack <twomack@chiark.greenend.org.uk> - 2011-10-23 19:30 +0100
                Re: big-little nmm1@cam.ac.uk - 2011-10-23 19:59 +0100
                Re: big-little BGB <cr88192@hotmail.com> - 2011-10-23 13:21 -0700
                Re: big-little Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-23 20:38 +0200
                Re: big-little nmm1@cam.ac.uk - 2011-10-23 22:38 +0100
                Re: big-little BGB <cr88192@hotmail.com> - 2011-10-23 17:56 -0700
                Re: big-little nmm1@cam.ac.uk - 2011-10-24 07:58 +0100
                Re: big-little BGB <cr88192@hotmail.com> - 2011-10-24 16:34 -0700
                Re: big-little nmm1@cam.ac.uk - 2011-10-25 08:09 +0100
                Re: big-little Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-25 14:52 +0200
                Re: big-little nmm1@cam.ac.uk - 2011-10-25 17:28 +0100
                Re: big-little BGB <cr88192@hotmail.com> - 2011-10-25 13:06 -0700
                Re: big-little BGB <cr88192@hotmail.com> - 2011-10-25 15:22 -0700
                Re: big-little "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-10-25 19:47 -0700
                Re: big-little nmm1@cam.ac.uk - 2011-10-26 08:09 +0100
                Re: big-little Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-26 12:06 +0200
                Re: big-little nmm1@cam.ac.uk - 2011-10-26 10:47 +0100
                Re: big-little Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-26 11:58 +0200
                Re: big-little nmm1@cam.ac.uk - 2011-10-26 10:44 +0100
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-26 03:45 -0700
                Re: big-little nmm1@cam.ac.uk - 2011-10-26 11:45 +0100
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-26 09:15 -0700
                Re: big-little "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-10-26 12:51 -0700
                Re: big-little Andrew Reilly <areilly---@bigpond.net.au> - 2011-10-26 11:45 +0000
                Re: big-little nmm1@cam.ac.uk - 2011-10-26 15:42 +0100
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-26 09:07 -0700
                Re: big-little "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-10-26 12:53 -0700
                Re: big-little nmm1@cam.ac.uk - 2011-10-26 21:05 +0100
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-26 13:20 -0700
                Re: big-little "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-10-26 17:55 -0700
                Re: big-little nmm1@cam.ac.uk - 2011-10-27 09:10 +0100
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-27 01:34 -0700
                Re: big-little nmm1@cam.ac.uk - 2011-10-27 10:29 +0100
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-27 04:28 -0700
                Re: big-little EricP <ThatWouldBeTelling@thevillage.com> - 2011-10-27 12:22 -0400
                Re: big-little timcaffrey@aol.com (Tim McCaffrey) - 2011-10-27 18:08 +0000
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-27 11:50 -0700
                Re: big-little Jean-Marc Bourguet <jm@bourguet.org> - 2011-10-27 14:10 +0200
                Re: big-little nmm1@cam.ac.uk - 2011-10-27 17:58 +0100
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-26 13:15 -0700
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-27 04:10 -0700
                Re: big-little MitchAlsup <MitchAlsup@aol.com> - 2011-10-27 14:04 -0700
                Re: big-little nmm1@cam.ac.uk - 2011-10-27 23:07 +0100
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-27 15:58 -0700
                Re: big-little Rick Jones <rick.jones2@hp.com> - 2011-10-27 22:57 +0000
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-27 16:39 -0700
                Re: big-little Rick Jones <rick.jones2@hp.com> - 2011-10-28 00:16 +0000
                Re: big-little nmm1@cam.ac.uk - 2011-10-28 09:52 +0100
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-28 07:01 -0700
                Re: big-little Rick Jones <rick.jones2@hp.com> - 2011-10-28 16:45 +0000
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-29 13:13 -0700
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-30 03:36 -0700
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-30 03:55 -0700
                Re: big-little MitchAlsup <MitchAlsup@aol.com> - 2011-10-28 11:15 -0700
                Re: big-little nmm1@cam.ac.uk - 2011-10-28 20:01 +0100
                Re: big-little timcaffrey@aol.com (Tim McCaffrey) - 2011-10-29 17:46 +0000
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-29 11:30 -0700
                Re: big-little nmm1@cam.ac.uk - 2011-10-29 20:02 +0100
                Re: big-little MitchAlsup <MitchAlsup@aol.com> - 2011-10-29 13:09 -0700
                Re: big-little "Paul A. Clayton" <paaronclayton@gmail.com> - 2011-10-29 17:42 -0700
                Re: big-little nmm1@cam.ac.uk - 2011-10-30 08:16 +0000
                Re: big-little MitchAlsup <MitchAlsup@aol.com> - 2011-11-04 10:06 -0700
                Re: big-little "Paul A. Clayton" <paaronclayton@gmail.com> - 2011-11-04 15:19 -0700
                Re: big-little nmm1@cam.ac.uk - 2011-11-05 09:13 +0000
                Re: big-little "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-11-05 09:03 -0700
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-26 13:38 -0700
                Re: big-little Robert Wessel <robertwessel2@yahoo.com> - 2011-10-26 18:44 -0500
                Re: big-little Michael S <already5chosen@yahoo.com> - 2011-10-26 17:05 -0700
                Re: big-little Robert Wessel <robertwessel2@yahoo.com> - 2011-10-26 21:03 -0500
                Re: big-little EricP <ThatWouldBeTelling@thevillage.com> - 2011-10-26 14:37 -0400
                Re: big-little EricP <ThatWouldBeTelling@thevillage.com> - 2011-10-26 15:38 -0400
                Re: big-little EricP <ThatWouldBeTelling@thevillage.com> - 2011-10-26 16:06 -0400
                Re: big-little BGB <cr88192@hotmail.com> - 2011-10-27 00:15 -0700
                Re: big-little Morten Reistad <first@last.name> - 2011-11-03 17:30 +0100
                Re: big-little "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-11-03 20:45 -0700
                Re: big-little Thomas Womack <twomack@chiark.greenend.org.uk> - 2011-11-04 11:13 +0000
                Re: big-little MitchAlsup <MitchAlsup@aol.com> - 2011-11-04 10:12 -0700
                Re: big-little BGB <cr88192@hotmail.com> - 2011-11-04 09:26 -0700
                Re: big-little EricP <ThatWouldBeTelling@thevillage.com> - 2011-11-05 11:32 -0400
                Re: big-little EricP <ThatWouldBeTelling@thevillage.com> - 2011-11-05 11:55 -0400
                Re: big-little BGB <cr88192@hotmail.com> - 2011-11-05 09:58 -0700
                Re: big-little Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-11-05 18:39 +0100
                Re: big-little BGB <cr88192@hotmail.com> - 2011-11-05 15:00 -0700
                Re: big-little wclodius@lost-alamos.pet (William Clodius) - 2011-11-05 18:43 -0600
                Re: big-little BGB <cr88192@hotmail.com> - 2011-11-05 19:46 -0700
                Re: big-little ChrisQ <meru@devnull.com> - 2011-11-11 12:31 +0000
                Re: big-little BGB <cr88192@hotmail.com> - 2011-11-11 12:39 -0700
                Re: big-little Chris Gray <cg@GraySage.com> - 2011-11-11 13:28 -0700
                Re: big-little BGB <cr88192@hotmail.com> - 2011-11-11 18:03 -0700
                Re: big-little Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-11-12 18:25 +0100
                Re: big-little BGB <cr88192@hotmail.com> - 2011-11-12 12:02 -0700
                cost of prolog/epilog (was: big-little) Kalle Olavi Niemitalo <kon@iki.fi> - 2011-11-12 22:57 +0200
                Re: cost of prolog/epilog Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-11-12 22:47 +0100
                Re: cost of prolog/epilog anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-11-14 09:45 +0000
                Re: cost of prolog/epilog Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-11-14 12:28 +0100
                Re: cost of prolog/epilog anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-11-15 16:48 +0000
                Re: cost of prolog/epilog Stefan Monnier <monnier@iro.umontreal.ca> - 2011-11-15 21:35 -0500
                Re: cost of prolog/epilog Bakul Shah <usenet@bitblocks.com> - 2011-11-16 02:41 -0800
                Re: cost of prolog/epilog nmm1@cam.ac.uk - 2011-11-16 18:14 +0000
                Re: cost of prolog/epilog BGB <cr88192@hotmail.com> - 2011-11-16 16:50 -0700
                Re: cost of prolog/epilog BGB <cr88192@hotmail.com> - 2011-11-14 17:00 -0700
                Re: cost of prolog/epilog torbenm@diku.dk (Torben Ægidius Mogensen) - 2011-11-15 10:26 +0100
                Re: cost of prolog/epilog BGB <cr88192@hotmail.com> - 2011-11-15 09:41 -0700
                Re: cost of prolog/epilog anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-11-15 16:40 +0000
                Re: cost of prolog/epilog Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-11-15 12:44 +0100
                Re: cost of prolog/epilog BGB <cr88192@hotmail.com> - 2011-11-15 09:01 -0700
                Re: cost of prolog/epilog Chris Gray <cg@GraySage.com> - 2011-11-15 15:18 -0700
                Re: cost of prolog/epilog BGB <cr88192@hotmail.com> - 2011-11-15 21:56 -0700
                Re: cost of prolog/epilog Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-11-16 09:21 +0100
                Re: cost of prolog/epilog anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-11-16 09:30 +0000
                Re: cost of prolog/epilog John Levine <johnl@iecc.com> - 2011-11-16 10:05 +0000
                Re: cost of prolog/epilog Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-11-16 11:08 +0100
                Re: cost of prolog/epilog Chris Gray <cg@GraySage.com> - 2011-11-16 16:29 -0700
                Re: cost of prolog/epilog BGB <cr88192@hotmail.com> - 2011-11-16 11:22 -0700
                Re: cost of prolog/epilog anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-11-17 13:27 +0000
                Re: cost of prolog/epilog BGB <cr88192@hotmail.com> - 2011-11-17 10:30 -0700
                Re: cost of prolog/epilog torbenm@diku.dk (Torben Ægidius Mogensen) - 2011-11-17 11:21 +0100
                Re: cost of prolog/epilog Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-11-17 11:56 +0100
                Re: cost of prolog/epilog timcaffrey@aol.com (Tim McCaffrey) - 2011-11-17 20:27 +0000
                Re: cost of prolog/epilog torbenm@diku.dk (Torben Ægidius Mogensen) - 2011-11-18 10:57 +0100
                Re: cost of prolog/epilog BGB <cr88192@hotmail.com> - 2011-11-17 10:42 -0700
                Re: cost of prolog/epilog (was: big-little) "Paul A. Clayton" <paaronclayton@gmail.com> - 2011-11-12 14:05 -0800
                Re: cost of prolog/epilog (was: big-little) Bernd Paysan <bernd.paysan@gmx.de> - 2011-11-18 02:39 +0100
                Re: cost of prolog/epilog torbenm@diku.dk (Torben Ægidius Mogensen) - 2011-11-18 10:59 +0100
                Re: cost of prolog/epilog Bernd Paysan <bernd.paysan@gmx.de> - 2011-11-18 22:06 +0100
                Re: cost of prolog/epilog (was: big-little) mac <acolvin@efunct.com> - 2011-11-20 23:01 +0000
                Re: cost of prolog/epilog Chris Gray <cg@GraySage.com> - 2011-11-13 13:35 -0700
                Re: big-little wclodius@lost-alamos.pet (William Clodius) - 2011-11-11 22:13 -0700
                Re: big-little BGB <cr88192@hotmail.com> - 2011-11-11 23:43 -0700
                Re: big-little Chris Gray <cg@GraySage.com> - 2011-11-12 14:08 -0700
                Re: big-little BGB <cr88192@hotmail.com> - 2011-11-12 19:10 -0700
                Re: big-little Chris Gray <cg@GraySage.com> - 2011-11-13 13:40 -0700
                Re: big-little Bakul Shah <usenet@bitblocks.com> - 2011-11-13 14:49 -0800
                Re: big-little BGB <cr88192@hotmail.com> - 2011-11-13 18:51 -0700
                Re: big-little Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-24 10:12 +0200
                Re: big-little Stefan Monnier <monnier@iro.umontreal.ca> - 2011-10-24 12:11 -0400
                Re: big-little "Paul A. Clayton" <paaronclayton@gmail.com> - 2011-10-24 10:28 -0700
                Re: big-little nospam@ab-katrinedal.dk (Niels Jørgen Kruse) - 2011-10-24 19:38 +0200
                Re: big-little Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-24 21:02 +0200
                Re: big-little "Paul A. Clayton" <paaronclayton@gmail.com> - 2011-10-23 12:02 -0700
        Re: big-little Morten Reistad <first@last.name> - 2011-11-03 00:51 +0100
    Re: big-little "Paul A. Clayton" <paaronclayton@gmail.com> - 2011-10-20 16:59 -0700
      Re: big-little Anne & Lynn Wheeler <lynn@garlic.com> - 2011-10-20 21:13 -0400
      Re: big-little nmm1@cam.ac.uk - 2011-10-21 08:01 +0100
        Re: big-little "Paul A. Clayton" <paaronclayton@gmail.com> - 2011-10-21 05:39 -0700
        Re: big-little torbenm@diku.dk (Torben Ægidius Mogensen) - 2011-10-24 10:18 +0200
      Re: big-little Pedro Pereira <ppereira@grupopie.com> - 2011-10-21 10:40 +0100
        Re: big-little Paul Gotch <paulg@at-cantab-dot.net> - 2011-10-21 12:42 +0100
    Re: big-little nik Simpson <nik_s@knology.net> - 2011-10-21 11:00 -0500
  Re: big-little Rick Jones <rick.jones2@hp.com> - 2011-10-20 21:13 +0000
    Re: big-little timcaffrey@aol.com (Tim McCaffrey) - 2011-10-20 21:43 +0000
    Re: big-little Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-21 09:23 +0200
      Re: big-little Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-10-21 14:35 +0200
        Re: big-little Rick Jones <rick.jones2@hp.com> - 2011-10-21 17:15 +0000
      Re: big-little BGB <cr88192@hotmail.com> - 2011-10-21 16:41 -0700
  Re: big-little jacko <jackokring@gmail.com> - 2011-10-26 14:12 -0700

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