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Re: Indirect Bit

From nmm1@cam.ac.uk
Newsgroups comp.arch
Subject Re: Indirect Bit
Date 2012-04-24 13:01 +0100
Organization Department of Deniable Assertions
Message-ID <jn64mo$5o2$1@needham.csi.cam.ac.uk> (permalink)
References <4F84FB1E.6CD1FC88@sonic.net> <5Hllr.64357$R85.25309@newsfe17.iad> <jn5l8i$1b3$1@needham.csi.cam.ac.uk> <56f11ed4-de0c-49b3-a56d-0b67554d0fe5@v1g2000yqm.googlegroups.com>

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In article <56f11ed4-de0c-49b3-a56d-0b67554d0fe5@v1g2000yqm.googlegroups.com>,
Michael S  <already5chosen@yahoo.com> wrote:
>>
>> My crude analyses are that maintaining the invariant that a single
>> location never goes backwards in time is easy, but that maintaining
>> definable and usable coherence model (e.g. sequential consistency)
>> is seriously antagonistic to scalability.
>
>My take on the issue is approximately like that:
>cache coherence done is hardware, is just a relatively efficient
>automatic implementation of generic optimization pattern known as
>leisure evaluation. I.e. cache coherence is a win as long as leisure
>evaluation strategy for cache line transfers is a win.

Assuming that you mean lazy evaluation, that's reasonable.

>Looking from that angle, usefulness of cache coherence hardware is
>almost independent of specific memory ordering model. After all,
>memory ordering model only influences the amount and  variate of
>explicit memory barriers that are necessary for correctness. So,
>memory ordering model could influence the win/loss balance only for
>corner cases of very fine-grain parallelism.

Your take has almost exactly the same flaw as that paper!

The killer is asynchronicity, which is a key to parallel scalability.
Lamport's original paper explained that serialising access at both
the CPUs and memory servers is enough for sequential consistency
but, if you have a LOT of them, that's precisely what you don't
want to have to do!  In particular, it makes a big difference if
you can allow write buffering and prefetching; Intel allows the
former.

The big trouble with understanding this is that it inherently the
global properties that cause the trouble, and so ANY serial analysis
(e.g. in that paper) is misleading.  And it is sufficiently hard that
decades of work haven't produced any definitive answer to whether
scalable sequential consistency is or is not possible.


Regards,
Nick Maclaren.

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Indirect Bit Mark Thorson <nospam@sonic.net> - 2012-04-10 19:31 -0800
  Re: Indirect Bit Robert Wessel <robertwessel2@yahoo.com> - 2012-04-11 01:29 -0500
    Re: Indirect Bit sarr.blumson@alum.dartmouth.org - 2012-04-11 14:48 +0000
      Re: Indirect Bit mac <acolvin@efunct.com> - 2012-04-12 14:43 +0000
    Re: Indirect Bit Morten Reistad <first@last.name> - 2012-04-22 15:19 +0200
      Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-22 23:24 -0700
  Re: Indirect Bit Terje Mathisen <"terje.mathisen at tmsw.no"> - 2012-04-11 08:32 +0200
    Re: Indirect Bit Michael S <already5chosen@yahoo.com> - 2012-04-11 05:49 -0700
      Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 21:22 -0700
        Re: Indirect Bit "Paul A. Clayton" <paaronclayton@gmail.com> - 2012-04-13 08:14 -0700
          Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-13 16:13 -0700
            Re: Indirect Bit "Paul A. Clayton" <paaronclayton@gmail.com> - 2012-04-13 20:01 -0700
              Re: Indirect Bit Andrew Reilly <areilly.---@bigpond.net.au> - 2012-04-14 03:16 +0000
                Re: Indirect Bit "Paul A. Clayton" <paaronclayton@gmail.com> - 2012-04-14 08:14 -0700
        Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-13 16:05 -0700
          Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-13 17:01 -0700
            Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-14 13:49 -0700
          Re: Indirect Bit Anne & Lynn Wheeler <lynn@garlic.com> - 2012-04-13 20:07 -0400
          Re: Indirect Bit Terje Mathisen <"terje.mathisen at tmsw.no"> - 2012-04-14 18:47 +0200
          Re: Indirect Bit Morten Reistad <first@last.name> - 2012-04-22 15:26 +0200
            Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-22 23:25 -0700
              Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-23 09:18 +0100
                Re: Indirect Bit EricP <ThatWouldBeTelling@thevillage.com> - 2012-04-23 19:35 -0400
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-24 08:37 +0100
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-24 09:42 +0100
                Re: Indirect Bit Michael S <already5chosen@yahoo.com> - 2012-04-24 01:58 -0700
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-24 11:26 +0100
                Re: Indirect Bit Michael S <already5chosen@yahoo.com> - 2012-04-24 05:02 -0700
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-24 13:58 +0100
                Re: Indirect Bit Michael S <already5chosen@yahoo.com> - 2012-04-24 10:07 -0700
                Re: Indirect Bit Michael S <already5chosen@yahoo.com> - 2012-04-24 04:30 -0700
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-24 13:01 +0100
  Re: Indirect Bit Stefan Monnier <monnier@iro.umontreal.ca> - 2012-04-11 10:03 -0400
  Re: Indirect Bit kenney@cix.compulink.co.uk - 2012-04-11 09:22 -0500
    Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-12 14:11 -0700
      Re: Indirect Bit Stefan Monnier <monnier@iro.umontreal.ca> - 2012-04-12 18:05 -0400
        Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 20:13 -0700
      Re: Indirect Bit Mark Thorson <nospam@sonic.net> - 2012-04-12 16:55 -0800
        Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-12 17:25 -0700
          Re: Indirect Bit Robert Wessel <robertwessel2@yahoo.com> - 2012-04-12 20:03 -0500
          Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 21:33 -0700
            Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-13 15:57 -0700
              Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-13 17:03 -0700
        Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 20:14 -0700
  Re: Indirect Bit Anne & Lynn Wheeler <lynn@garlic.com> - 2012-04-11 10:35 -0400
  Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-11 08:54 -0700
  Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 07:55 -0700
    Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-12 10:16 -0700
      Re: Indirect Bit jacko <jackokring@gmail.com> - 2012-04-12 11:07 -0700
        Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 21:34 -0700
      Re: Indirect Bit Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2012-04-12 11:35 -0700
        Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 21:41 -0700
          Re: Indirect Bit jacko <jackokring@gmail.com> - 2012-04-13 14:52 -0700
          Re: Indirect Bit Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2012-04-15 09:24 -0700
            Re: Indirect Bit Terje Mathisen <"terje.mathisen at tmsw.no"> - 2012-04-15 22:45 +0200
              Re: Indirect Bit Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2012-04-15 18:04 -0700
      Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-12 21:12 -0700
    Re: Indirect Bit timcaffrey@aol.com (Tim McCaffrey) - 2012-04-12 19:23 +0000
    Re: Indirect Bit Terje Mathisen <"terje.mathisen at tmsw.no"> - 2012-04-13 08:54 +0200
      Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-14 14:37 -0700
    Re: Indirect Bit Andrew Reilly <areilly.---@bigpond.net.au> - 2012-04-15 23:42 +0000
      Re: Indirect Bit "Paul A. Clayton" <paaronclayton@gmail.com> - 2012-04-16 08:08 -0700
        Re: Indirect Bit Andrew Reilly <areilly.---@bigpond.net.au> - 2012-04-16 23:38 +0000
          Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-16 21:29 -0700
      Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-16 21:25 -0700
  Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-12 14:05 -0700
    Re: Indirect Bit ChrisQ <blackhole@devnull.com> - 2012-04-14 10:12 +0000
      Re: Indirect Bit "Paul A. Clayton" <paaronclayton@gmail.com> - 2012-04-14 06:25 -0700
        Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-14 14:50 +0100
          Re: Indirect Bit ChrisQ <blackhole@devnull.com> - 2012-04-14 18:01 +0000
            Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-14 14:00 -0700
              Re: Indirect Bit Anne & Lynn Wheeler <lynn@garlic.com> - 2012-04-14 20:58 -0400
            Re: Indirect Bit "Paul A. Clayton" <paaronclayton@gmail.com> - 2012-04-16 09:57 -0700
            Re: Indirect Bit timcaffrey@aol.com (Tim McCaffrey) - 2012-04-20 23:19 +0000
          Re: Indirect Bit "Paul A. Clayton" <paaronclayton@gmail.com> - 2012-04-16 08:50 -0700
            Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-16 18:09 +0100
              Re: Indirect Bit Andrew Reilly <areilly.---@bigpond.net.au> - 2012-04-16 23:19 +0000
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-17 09:20 +0100
                Re: Indirect Bit Terje Mathisen <"terje.mathisen at tmsw.no"> - 2012-04-17 12:49 +0200
                Re: Indirect Bit Andrew Reilly <areilly.---@bigpond.net.au> - 2012-04-17 12:40 +0000
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-18 12:01 +0100
                Re: Indirect Bit anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-04-17 12:34 +0000
                Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-17 09:10 -0700
                Re: Indirect Bit Andrew Reilly <areilly.---@bigpond.net.au> - 2012-04-17 22:05 +0000
                Re: Indirect Bit jgk@panix.com (Joe keane) - 2012-04-19 19:37 +0000
                Re: Indirect Bit torbenm@diku.dk (Torben Ægidius Mogensen) - 2012-04-20 11:10 +0200
                Re: Indirect Bit Terje Mathisen <"terje.mathisen at tmsw.no"> - 2012-04-20 11:24 +0200
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-20 15:01 +0100
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-20 15:03 +0100
                Re: Indirect Bit Michael S <already5chosen@yahoo.com> - 2012-04-20 08:01 -0700
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-20 16:35 +0100
                Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-18 11:10 -0700
                Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-18 15:37 -0700
          Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-16 11:21 -0700
            Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-16 19:36 +0100
              Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-18 11:17 -0700
                Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-18 15:33 -0700
                Re: Indirect Bit Andreas Eder <andreas_eder@gmx.net> - 2012-04-19 00:29 +0200
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-19 10:50 +0100
                Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-19 11:29 -0700
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-19 21:39 +0100
                Re: Indirect Bit EricP <ThatWouldBeTelling@thevillage.com> - 2012-04-20 15:14 -0400
                Re: Indirect Bit "Andy (Super) Glew" <andy@SPAM.comp-arch.net> - 2012-04-20 22:43 -0700
                Re: Indirect Bit EricP <ThatWouldBeTelling@thevillage.com> - 2012-04-21 17:14 -0400
                Re: Indirect Bit Robert Wessel <robertwessel2@yahoo.com> - 2012-04-21 19:47 -0500
                Re: Indirect Bit Nomen Nescio <nobody@dizum.com> - 2012-04-22 10:45 +0200
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-22 09:57 +0100
                Re: Indirect Bit Terje Mathisen <"terje.mathisen at tmsw.no"> - 2012-04-22 12:54 +0200
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-22 13:00 +0100
                Re: Indirect Bit Nomen Nescio <nobody@dizum.com> - 2012-04-22 13:28 +0200
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-22 13:04 +0100
                Re: Indirect Bit Fritz Wuehler <fritz@spamexpire-201204.rodent.frell.theremailer.net> - 2012-04-22 23:00 +0200
                Re: Indirect Bit Anne & Lynn Wheeler <lynn@garlic.com> - 2012-04-22 18:05 -0400
                Re: Indirect Bit glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-04-22 23:20 +0000
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-23 08:22 +0100
                Re: Indirect Bit Michael S <already5chosen@yahoo.com> - 2012-04-22 03:56 -0700
                Re: Indirect Bit EricP <ThatWouldBeTelling@thevillage.com> - 2012-04-22 12:28 -0400
                Re: Indirect Bit Robert Wessel <robertwessel2@yahoo.com> - 2012-04-22 12:56 -0500
                Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-22 13:15 -0700
                Re: Indirect Bit Nomen Nescio <nobody@dizum.com> - 2012-04-22 22:30 +0200
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-22 21:40 +0100
                Re: Indirect Bit Robert Wessel <robertwessel2@yahoo.com> - 2012-04-22 17:15 -0500
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-23 08:26 +0100
                Re: Indirect Bit Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2012-04-23 08:02 -0700
                Re: Indirect Bit nmm1@cam.ac.uk - 2012-04-23 17:02 +0100
                Re: Indirect Bit Fritz Wuehler <fritz@spamexpire-201204.rodent.frell.theremailer.net> - 2012-04-23 20:17 +0200
                Re: Indirect Bit Robert Wessel <robertwessel2@yahoo.com> - 2012-04-23 13:07 -0500
                Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-22 13:16 -0700
                Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-23 13:14 -0700
                Re: Indirect Bit Anne & Lynn Wheeler <lynn@garlic.com> - 2012-04-23 16:51 -0400
                Re: Indirect Bit Quadibloc <jsavard@ecn.ab.ca> - 2012-04-23 14:22 -0700
                Re: Indirect Bit MitchAlsup <MitchAlsup@aol.com> - 2012-04-21 11:17 -0700
        Re: Indirect Bit jacko <jackokring@gmail.com> - 2012-04-14 08:02 -0700

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