Re: RAFTS-like optimiser; progress report

From	anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups	comp.lang.forth
Subject	Re: RAFTS-like optimiser; progress report
Date	2013-09-11 15:21 +0000
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID	<2013Sep11.172119@mips.complang.tuwien.ac.at> (permalink)
References	(3 earlier) <laqdnaQ8I6t7CLbPnZ2dnUVZ_q2XnZ2d@supernews.com> <2013Sep9.144131@mips.complang.tuwien.ac.at> <DKydncrylYLrTrDPnZ2dnUVZ_gWdnZ2d@supernews.com> <2013Sep9.170811@mips.complang.tuwien.ac.at> <_vmdnVjAG8aecLDPnZ2dnUVZ_oudnZ2d@supernews.com>

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Andrew Haley <andrew29@littlepinkcloud.invalid> writes:
>Anton Ertl <anton@mips.complang.tuwien.ac.at> wrote:
>> Yes, it is likely, that, if processor makers make their hardware
>> better, the number of programmers who can implement lockless code
>> correctly rises from <1000 to maybe 100000, which will still be a
>> minority of programmers, and most programmers will still use
>> higher-level libraries.
>
>The hardware isn't going to change wrt memory consistency, from what
>I've seen of newish designs.  What we are going to get instead,
>though, is hardware support for transactions.  Then you don't need to
>support memory consistency where it isn't necessary.
>
>> And I think that the processor makers will make their hardware
>> better, because they want to sell multi-cores, and the more
>> programmers are out there that can make good use of them, the more
>> applications will there be that are an argument for buying them.
>
>For some value of "better", yes, but not in the way you're suggesting.
>Maintaining a consistent view of memory all the time across all cores
>is too expensive.

Precise exceptions are too expensive, so Alpha has the (originally
expensive) TRAPB instruction.  Eventually they implemented precise
exceptions, and TRAPB became a noop.  Byte and 16-bit accesses are too
expensive, so Alpha did not implement them.  Eventually they were
added to Alpha.  Cache-coherence shared memory for more than ~16 CPUs
is too expensive, so supercomputers are using private memory nodes
(called "massively parallel processors").  Then directory-based cache
coherence (NUMA) was developed, and last I heard up to 1024 CPUs were
possible in a shared-memory machine (maybe more these days), and even
supercomputers used that.

I am confident that the hardware people can make hardware that has a
reasonable consistency model if they put their minds to it.

The weakly consistent models do not cut it, though; they may be ok for
some academics who have a nice puzzle to solve for writing a paper on
a small problem, but for producing software they are too complex.
Telling the programmers: "Your code will be correct if you use
barriers everywhere.  Your code will be dog-slow if you use barriers
everywhere." does not lead to correct and fast programs.

You may be right, and the hardware guys may find a different way to
give programmers an understandable way to program with shared memory,
and if that way is cheaper to implement than a reasonable consistency
model, then yes, the reasonable consistency model will be too
expensive.  But if the hardware guys tell us: "Your code will be
correct if you use transactions everywhere.  Your code will be
dog-slow if you use transactions everywhere.", then transactions won't
cut it, either.

- anton
-- 
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
     New standard: http://www.forth200x.org/forth200x.html
   EuroForth 2013: http://www.euroforth.org/ef13/

Thread

RAFTS-like optimiser; progress report Alex McDonald <blog@rivadpm.com> - 2013-09-06 14:12 -0700
  Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-06 16:54 -0500
    Re: RAFTS-like optimiser; progress report Alex McDonald <blog@rivadpm.com> - 2013-09-06 16:02 -0700
      Re: RAFTS-like optimiser; progress report Bernd Paysan <bernd.paysan@gmx.de> - 2013-09-07 03:01 +0200
        Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-07 03:21 -0500
          Re: RAFTS-like optimiser; progress report albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-09-07 19:56 +0000
    Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-07 15:06 +0000
      Re: RAFTS-like optimiser; progress report "Alex McDonald" <blog@rivadpm.com> - 2013-09-07 19:01 +0100
        Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-09 12:23 +0000
          Re: RAFTS-like optimiser; progress report "Alex McDonald" <blog@rivadpm.com> - 2013-09-10 12:01 +0100
            Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-10 12:45 +0000
              Re: RAFTS-like optimiser; progress report "Alex McDonald" <blog@rivadpm.com> - 2013-09-10 16:33 +0100
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-11 15:02 +0000
                Re: RAFTS-like optimiser; progress report "Alex McDonald" <blog@rivadpm.com> - 2013-09-11 17:44 +0100
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-13 11:58 +0000
                Re: RAFTS-like optimiser; progress report "Rod Pemberton" <dont_use_email@nohavenotit.com> - 2013-09-14 22:47 -0400
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-15 16:05 +0000
      Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-07 16:08 -0500
        Re: RAFTS-like optimiser; progress report mhx@iae.nl - 2013-09-08 03:21 -0700
          Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-08 06:42 -0500
            Re: RAFTS-like optimiser; progress report mhx@iae.nl - 2013-09-08 04:51 -0700
              Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-08 07:02 -0500
                Re: RAFTS-like optimiser; progress report Paul Rubin <no.email@nospam.invalid> - 2013-09-08 10:08 -0700
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-08 12:47 -0500
                Re: RAFTS-like optimiser; progress report Paul Rubin <no.email@nospam.invalid> - 2013-09-08 11:10 -0700
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-08 15:16 -0500
                Re: RAFTS-like optimiser; progress report Paul Rubin <no.email@nospam.invalid> - 2013-09-08 16:08 -0700
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-09 04:57 -0500
        Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-09 12:41 +0000
          Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-09 08:56 -0500
            Re: RAFTS-like optimiser; progress report albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-09-09 14:20 +0000
              Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-09 09:27 -0500
                Re: RAFTS-like optimiser; progress report "Rod Pemberton" <dont_use_email@nohavenotit.com> - 2013-09-10 04:31 -0400
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-10 05:11 -0500
            Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-09 15:08 +0000
              Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-09 10:45 -0500
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-11 15:21 +0000
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-11 12:04 -0500
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-11 17:46 +0000
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-11 14:45 -0500
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-13 13:00 +0000
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-13 10:46 -0500
                Re: RAFTS-like optimiser; progress report stephenXXX@mpeforth.com (Stephen Pelc) - 2013-09-13 17:44 +0000
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-14 15:31 +0000
                Re: RAFTS-like optimiser; progress report Paul Rubin <no.email@nospam.invalid> - 2013-09-14 10:33 -0700
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-14 12:39 -0500
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-15 15:05 +0000
                Re: RAFTS-like optimiser; progress report Alex McDonald <blog@rivadpm.com> - 2013-09-15 08:32 -0700
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-15 13:20 -0500
                Re: RAFTS-like optimiser; progress report stephenXXX@mpeforth.com (Stephen Pelc) - 2013-09-15 16:54 +0000
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-15 17:02 +0000
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-15 12:54 -0500
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-16 09:21 +0000
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-16 08:39 -0500
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-16 15:48 +0000
                Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-16 15:03 -0500
                Re: RAFTS-like optimiser; progress report anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-09-17 10:15 +0000
                Re: RAFTS-like optimiser; progress report "Rod Pemberton" <dont_use_email@nohavenotit.com> - 2013-09-17 17:24 -0400
                Re: RAFTS-like optimiser; progress report stephenXXX@mpeforth.com (Stephen Pelc) - 2013-09-17 13:10 +0000
            Re: RAFTS-like optimiser; progress report "Rod Pemberton" <dont_use_email@nohavenotit.com> - 2013-09-10 04:30 -0400
              Re: RAFTS-like optimiser; progress report Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-09-10 05:14 -0500
  Re: RAFTS-like optimiser; progress report mhx@iae.nl - 2013-09-07 03:22 -0700
  Re: RAFTS-like optimiser; progress report mhx@iae.nl - 2013-09-07 03:32 -0700

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