Re: Notions of Time in Computer Architecture

Message-ID	<4E0D5E34.1030600@SPAM.comp-arch.net> (permalink)
Date	2011-06-30 22:42 -0700
From	"Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net>
Organization	comp-arch.net
Newsgroups	comp.arch
Subject	Re: Notions of Time in Computer Architecture
References	<4E0BA344.6000003@SPAM.comp-arch.net> <6s5ud8-ikv2.ln1@ntp6.tmsw.no>

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On 6/30/2011 5:13 AM, Terje Mathisen wrote:
> Andy "Krazy" Glew wrote:
>> First, there is [[real time]] or [[wall clock time]]. Time in the real
>> world (forgetting Einsteinian relativistic issues for the moment).
>
> With the sub-ns time scales in modern cpus, any large cluster (even if
> presented as a single image CC-NUMA system to the programmer) will get
> into trouble here:
>
> You cannot have a globally consistent, totally distributed clock: Unless
> you designate a single point of control, there's no way to always be
> able to figure out the absolute order of two or more distributed events,
> right?
>
> You simply have to fall back on workarounds, like having N bits for the
> clock, of which the lower M bits is the clock ID. This way all
> timestamps will be globally unique and sortable, even if the resulting
> order might not be the "real" order as observed by some omniscient entity.
>
> Terje
>


I think Lamport clocks are probably buildable - wasn't it Mark Hill 
and/or David Wood who have a paper on that?  But whether it is worth 
building them is another question.

Myself, I doubt that it is worth the effort to have synchronized the 
clocks in shared memory systems.

Thread

Notions of Time in Computer Architecture "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-06-29 15:12 -0700
  Re: Notions of Time in Computer Architecture Robert Myers <rbmyersusa@gmail.com> - 2011-06-29 22:08 -0400
  Re: Notions of Time in Computer Architecture Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-06-30 14:13 +0200
    Re: Notions of Time in Computer Architecture Morten Reistad <first@last.name> - 2011-06-30 18:19 +0200
    Re: Notions of Time in Computer Architecture ChrisQ <meru@devnull.com> - 2011-06-30 21:23 +0100
      Re: Notions of Time in Computer Architecture Rick Jones <rick.jones2@hp.com> - 2011-06-30 19:42 +0000
        Re: Notions of Time in Computer Architecture Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-07-01 10:46 +0200
          Re: Notions of Time in Computer Architecture Rick Jones <rick.jones2@hp.com> - 2011-07-01 15:17 +0000
            Re: Notions of Time in Computer Architecture ChrisQ <meru@devnull.com> - 2011-07-04 16:51 +0100
      Re: Notions of Time in Computer Architecture nmm1@cam.ac.uk - 2011-07-01 05:54 +0100
    Re: Notions of Time in Computer Architecture "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-06-30 22:42 -0700
    Re: Notions of Time in Computer Architecture jsavard@excxn.aNOSPAMb.cdn.invalid (John Savard) - 2011-07-01 20:16 +0000
      Re: Notions of Time in Computer Architecture Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-07-02 10:33 +0200
        Re: Notions of Time in Computer Architecture nmm1@cam.ac.uk - 2011-07-02 09:26 +0100
        Re: Notions of Time in Computer Architecture jsavard@excxn.aNOSPAMb.cdn.invalid (John Savard) - 2011-07-02 12:40 +0000
          Re: Notions of Time in Computer Architecture nmm1@cam.ac.uk - 2011-07-02 16:14 +0100
          Re: Notions of Time in Computer Architecture Robert Myers <rbmyersusa@gmail.com> - 2011-07-02 16:48 -0400
            Re: Notions of Time in Computer Architecture Quadibloc <jsavard@ecn.ab.ca> - 2011-07-02 14:27 -0700
              Re: Notions of Time in Computer Architecture Stephen Sprunk <stephen@sprunk.org> - 2011-07-03 15:07 -0500
                Re: Notions of Time in Computer Architecture Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-07-04 08:15 +0200
                Re: Notions of Time in Computer Architecture Morten Reistad <first@last.name> - 2011-07-04 17:50 +0200
                Re: Notions of Time in Computer Architecture Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-07-04 21:21 +0200
                Re: Notions of Time in Computer Architecture Robert Wessel <robertwessel2@yahoo.com> - 2011-07-04 23:44 -0500
                Re: Notions of Time in Computer Architecture Terje Mathisen <"terje.mathisen at tmsw.no"> - 2011-07-05 07:51 +0200
                Re: Notions of Time in Computer Architecture Robert Wessel <robertwessel2@yahoo.com> - 2011-07-05 01:56 -0500
            Re: Notions of Time in Computer Architecture Morten Reistad <first@last.name> - 2011-07-03 19:28 +0200
          Re: Notions of Time in Computer Architecture "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-07-03 11:27 -0700
            Re: Notions of Time in Computer Architecture nmm1@cam.ac.uk - 2011-07-03 22:13 +0100
              Re: Notions of Time in Computer Architecture "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-07-03 18:53 -0700
                Re: Notions of Time in Computer Architecture nmm1@cam.ac.uk - 2011-07-04 08:34 +0100
            Re: Notions of Time in Computer Architecture "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-07-03 18:51 -0700
            Re: Notions of Time in Computer Architecture anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-07-04 09:20 +0000
              Re: Notions of Time in Computer Architecture Robert Myers <rbmyersusa@gmail.com> - 2011-07-04 12:26 -0700
                Re: Notions of Time in Computer Architecture EricP <ThatWouldBeTelling@thevillage.com> - 2011-07-04 19:35 -0400
                Re: Notions of Time in Computer Architecture Bernd Paysan <bernd.paysan@gmx.de> - 2011-07-08 15:48 +0200
            Re: Notions of Time in Computer Architecture Michael S <already5chosen@yahoo.com> - 2011-07-05 15:24 -0700
              Re: Notions of Time in Computer Architecture "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-07-08 09:25 -0700
                Re: Notions of Time in Computer Architecture Robert Myers <rbmyersusa@gmail.com> - 2011-07-08 12:12 -0700
                Re: Notions of Time in Computer Architecture "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-07-08 17:27 -0700
                Re: Notions of Time in Computer Architecture Robert Myers <rbmyersusa@gmail.com> - 2011-07-09 18:07 -0400
                Re: Notions of Time in Computer Architecture EricP <ThatWouldBeTelling@thevillage.com> - 2011-07-10 12:03 -0400
                Re: Notions of Time in Computer Architecture Robert Myers <rbmyersusa@gmail.com> - 2011-07-10 13:02 -0700
    Re: Notions of Time in Computer Architecture Bernd Paysan <bernd.paysan@gmx.de> - 2011-07-08 15:13 +0200
  Re: Notions of Time in Computer Architecture Gubbi <gubsan100@hotmail.com> - 2011-07-01 00:50 -0700

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