Re: Notions of Time in Computer Architecture

From	jsavard@excxn.aNOSPAMb.cdn.invalid (John Savard)
Newsgroups	comp.arch
Subject	Re: Notions of Time in Computer Architecture
Date	2011-07-02 12:40 +0000
Organization	Aioe.org NNTP Server
Message-ID	<4e0f0fb6.148514@news.aioe.org> (permalink)
References	<4E0BA344.6000003@SPAM.comp-arch.net> <6s5ud8-ikv2.ln1@ntp6.tmsw.no> <4e0e2a2f.820481@news.aioe.org> <ko13e8-bm4.ln1@ntp6.tmsw.no>

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On Sat, 02 Jul 2011 10:33:53 +0200, Terje Mathisen <"terje.mathisen at
tmsw.no"> wrote, in part:

>John, please re-read what I wrote:
>
>Having a single clock source is of course doable, what I claimed was 
>that with a totally distributed setup, i.e. _no_ central distribution 
>point, you can't do the same.

It is indeed true that I didn't fully address your real point, and that
I even may have misunderstood part of what you wrote.

>OTOH, even with a central clock there's no way to guarantee that you can 
>determine the absolute order of distributed events, you must also have a 
>central time stamp authority, and that would be an impossible bottleneck.

Multiple synchronized time stamp authorities, of course, could establish
order down to some minimal granularity below which events are seen as
simultaneous.

>You always end up with the need for some other way (i.e. something like 
>a cpu id) to arbitrate between "close enough" events, things that happen 
>within the clock resolution steps.

But you've noted this. One thing, though; with a single clock, "close
enough" really is simultaneous.

>Add in relativity and you realize that it might not be even 
>theoretically possible to determine which of two events happened "first".

Silly me. I was thinking in terms of parallel computers that are wired
together and sitting on a floor somewhere, if not bolted to it. So a
default reference frame would be obvious.

Due to extreme propagation delays, a network of computers spanning the
Solar System would not normally serve for tightly-coupled calculations.
But someday such things might have applications at least as
communications networks... and why shouldn't someone on Mars join in one
of those "@home" projects, since embarassingly parallel problems don't
have propagation to worry about much?

So it could indeed be that relativistic considerations would someday
impact the definition of priority...

John Savard
http://www.quadibloc.com/index.html

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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