Re: GA144 use cases

From	anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups	comp.lang.forth
Subject	Re: GA144 use cases
Date	2015-09-03 16:11 +0000
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID	<2015Sep3.181126@mips.complang.tuwien.ac.at> (permalink)
References	(6 earlier) <ms7sg0$78f$1@dont-email.me> <5a1458c0-a2b6-4f63-8ea0-57b7f19aa41f@googlegroups.com> <34f1f225-c6e9-47e7-91cb-ba225d5d9bca@googlegroups.com> <2015Sep3.123542@mips.complang.tuwien.ac.at> <ms9jb8$fre$1@dont-email.me>

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Bernd Paysan <bernd.paysan@gmx.de> writes:
>Anton Ertl wrote:
>> And the same goes for paragraphs.  OTOH, TeX is so fast on modern CPUs
>> that one can really say that paralellizing it would not enhance it.
>> Also, parallelizing it would require quite a bit of effort.
>
>Well, TeX is written in an "unmaintainable" programming language, c-web.  
>Let's go with the paragraphs: TeX tries to render the paragraph with several 
>different attempts, and chooses the best-"looking", with a metric of what is 
>"best".  That is fairly easy to parallelize, you just run all the trials in 
>parallel, and then collect the results.  The one with the lowest badness 
>wins, and the others get deleted.

And you can do many paragraphs in parallel.

>The problem with parallelism I have is not that I can't imagine it, but that 
>the overhead is too large.  E.g. take net2o:  I send and receive messages 
>(each takes time in the kernel), and I decrypt and encrypt them.  With a 
>four-core CPU, I could run that in four tasks.
>
>However, when trying that, I found that the IPC is killing the performance.  
>These tasks don't take too much time - en/decrypting a 1k block takes 10k 
>cycles, and the IPC then takes about as long, too, so all the gain goes down 
>the flush.
>
>What we need for this sort of lightweight tasks done in parallel is a 
>lightweight, fast, in-hardware IPC, similar in spirit to the GA144 
>connections or Transputer links.

If it's just communication, that can go pretty fast through shared
memory; on a single-socket multi-core CPU, that's a trip through the
L3 cache (<100 cycles latency for the first cache line; and you can
communicate pretty long blocks with pretty low additional overhead).

If it's synchronization, that's a bit more expensive, but also
determined by L3 latency in such a system if you do it on the user
level (with locked instructions or similar).

If you manage to use large blocks and synchronization is rare, you can
make good use of multiple cores.  OTOH, if you need to create lots of
short-running tasks and combine their results, you will probably see a
lot of overhead.

>The next issue I have is that the shared memory approach is broken, it is 
>way too hard to debug.

Yes, especially with the perverse consistency models that some
architectures provide.  But as a primitive for better models (such as
pipelining), it's not too bad.  I first thought that one would need
something like links for implementing pipelines, but it can be done
with shared memory.

>  I'd prefer a single-writer, multiple reader shared 
>memory approach, so each process would have its writable memory, and all 
>other threads can only read that.  You may have common shared memory for 
>something like the root pointers of RCU trees (you can read and copy from 
>other nodes into your own writable memory, and then update the root 
>pointer), which need more care, but most of the memory really shouldn't be 
>writable by every thread.  A common address space is still ok.
>
>That could be done with some more fields in the page table entry, having 
>access rights for the thread itself and others.  The thread itself is 
>identified by some higher bits in the virtual address, so the property "this 
>thread" vs "other threads" is decided by the first level page table.

You can get that by mmap()ing the memory once read-only and once
read/write.  If you want to mmapt them to the same address, I think
you need to do that in two different processes.

But that would still expose the programs to the perversities of the
consistency models.

- 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 2015: http://www.rigwit.co.uk/EuroForth2015/

Thread

GA144 use cases dunno <dunno@dunno.dunno> - 2015-08-31 07:20 +0000
  Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-08-31 09:55 -0400
  Re: GA144 use cases Syd Rumpo <usenet@nononono.co.uk> - 2015-08-31 16:49 +0100
    Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-08-31 18:35 -0400
  Re: GA144 use cases Dennis Ruffer <daruffer@gmail.com> - 2015-08-31 19:08 -0700
    Re: GA144 use cases Mux <Yvo.Zoer@gmail.com> - 2015-09-02 10:57 -0700
      Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-02 14:17 -0400
        Re: GA144 use cases Mux <Yvo.Zoer@gmail.com> - 2015-09-02 11:28 -0700
          Re: GA144 use cases hughaguilar96@gmail.com - 2015-09-02 13:41 -0700
          Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-02 16:50 -0400
            Re: GA144 use cases Mux <Yvo.Zoer@gmail.com> - 2015-09-02 15:03 -0700
              Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-02 18:18 -0400
                Re: GA144 use cases Mux <Yvo.Zoer@gmail.com> - 2015-09-02 16:14 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-02 20:40 -0400
                Re: GA144 use cases Greg <borota@gmail.com> - 2015-09-02 17:53 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-02 21:25 -0400
                Re: GA144 use cases Mux <Yvo.Zoer@gmail.com> - 2015-09-02 22:28 -0700
                Re: GA144 use cases Paul Rubin <no.email@nospam.invalid> - 2015-09-02 22:53 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-03 11:32 -0400
                Re: GA144 use cases Paul Rubin <no.email@nospam.invalid> - 2015-09-03 11:57 -0700
                Re: GA144 use cases anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-09-03 10:35 +0000
                Re: GA144 use cases Bernd Paysan <bernd.paysan@gmx.de> - 2015-09-03 15:54 +0200
                Re: GA144 use cases anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-09-03 16:11 +0000
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-03 13:06 -0400
                Re: GA144 use cases anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-09-04 08:07 +0000
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-04 11:49 -0400
                Re: GA144 use cases anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-09-05 11:06 +0000
                Re: GA144 use cases Paul Rubin <no.email@nospam.invalid> - 2015-09-05 09:05 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-05 12:59 -0400
                Re: GA144 use cases mhx@iae.nl - 2015-09-05 10:56 -0700
                Re: GA144 use cases anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-09-06 14:29 +0000
                Re: GA144 use cases Bernd Paysan <bernd.paysan@gmx.de> - 2015-09-03 22:08 +0200
                Re: GA144 use cases Paul Rubin <no.email@nospam.invalid> - 2015-09-03 14:00 -0700
                Re: GA144 use cases Bernd Paysan <bernd.paysan@gmx.de> - 2015-09-04 01:28 +0200
                Re: GA144 use cases franck.bensusan@gmail.com - 2015-09-03 23:04 -0700
                Re: GA144 use cases anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-09-04 08:24 +0000
                Re: GA144 use cases Bernd Paysan <bernd.paysan@gmx.de> - 2015-09-04 15:09 +0200
                Re: GA144 use cases anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-09-05 15:10 +0000
                Re: GA144 use cases Bernd Paysan <bernd.paysan@gmx.de> - 2015-09-05 22:04 +0200
                Re: GA144 use cases anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-09-06 14:51 +0000
                Re: GA144 use cases Bernd Paysan <bernd.paysan@gmx.de> - 2015-09-06 22:51 +0200
                Re: GA144 use cases Greg <borota@gmail.com> - 2015-09-06 17:30 -0700
                Re: GA144 use cases Paul Rubin <no.email@nospam.invalid> - 2015-09-04 22:27 -0700
                Re: GA144 use cases Bernd Paysan <bernd.paysan@gmx.de> - 2015-09-05 13:07 +0200
                Re: GA144 use cases anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-09-05 11:22 +0000
                Re: GA144 use cases anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-09-04 08:14 +0000
                Re: GA144 use cases Bernd Paysan <bernd.paysan@gmx.de> - 2015-09-04 15:13 +0200
                Re: GA144 use cases anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-09-05 16:06 +0000
                Re: GA144 use cases Bernd Paysan <bernd.paysan@gmx.de> - 2015-09-05 21:05 +0200
                Re: GA144 use cases anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-09-06 14:37 +0000
                Re: GA144 use cases Andrew Haley <andrew29@littlepinkcloud.invalid> - 2015-11-30 04:17 -0600
                Re: GA144 use cases Bernd Paysan <bernd.paysan@gmx.de> - 2015-12-01 23:06 +0100
                Re: GA144 use cases Mark Wills <markwills1970@gmail.com> - 2015-09-03 00:05 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-03 13:08 -0400
              Re: GA144 use cases forther <forther@gmail.com> - 2015-09-07 11:26 -0700
      Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-02 15:15 -0400
    Re: GA144 use cases forther <forther@gmail.com> - 2015-09-07 11:21 -0700
      Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-11-30 16:33 -0500
        Re: GA144 use cases forther <forther@gmail.com> - 2015-12-03 12:12 -0800
          Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-12-03 16:10 -0500
  Re: GA144 use cases Jason Damisch <jasondamisch@yahoo.com> - 2015-09-02 12:10 -0700
  Re: GA144 use cases Stefan Mauerhofer <smauerhofer@androsoft.ch> - 2015-09-03 01:27 -0700
    Re: GA144 use cases Syd Rumpo <usenet@nononono.co.uk> - 2015-09-03 13:32 +0100
      Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-03 11:32 -0400
  Re: GA144 use cases mhx@iae.nl (Marcel Hendrix) - 2015-09-03 18:57 +0200
    Re: GA144 use cases Bernd Paysan <bernd.paysan@gmx.de> - 2015-09-03 23:58 +0200
    Re: GA144 use cases anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-09-04 07:52 +0000
    Re: GA144 use cases Waldek Hebisch <hebisch@antispam.uni.wroc.pl> - 2015-09-05 16:32 +0000
      Re: GA144 use cases mhx@iae.nl - 2015-09-05 10:52 -0700
        Re: GA144 use cases Bernd Paysan <bernd.paysan@gmx.de> - 2015-09-05 22:11 +0200
          Re: GA144 use cases anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-09-06 14:18 +0000
            Re: GA144 use cases anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-09-07 07:49 +0000
        Re: GA144 use cases Waldek Hebisch <hebisch@math.uni.wroc.pl> - 2015-09-05 23:42 +0000
          Re: GA144 use cases Paul Rubin <no.email@nospam.invalid> - 2015-09-05 17:25 -0700
  Re: GA144 use cases Stefan Mauerhofer <smauerhofer@androsoft.ch> - 2015-09-07 03:18 -0700
    Re: GA144 use cases Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-09-07 03:31 -0700
      Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-07 15:06 -0400
        Re: GA144 use cases Stefan Mauerhofer <smauerhofer@androsoft.ch> - 2015-09-08 21:41 -0700
          Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-09 02:54 -0400
            Re: GA144 use cases Stefan Mauerhofer <smauerhofer@androsoft.ch> - 2015-09-09 03:02 -0700
              Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-09 16:55 -0400
                Re: GA144 use cases Paul Rubin <no.email@nospam.invalid> - 2015-09-09 20:12 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-09 23:40 -0400
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-09 23:43 -0400
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-10 00:07 -0400
                Re: GA144 use cases Stefan Mauerhofer <smauerhofer@androsoft.ch> - 2015-09-09 21:55 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-10 01:43 -0400
                Re: GA144 use cases Stefan Mauerhofer <smauerhofer@androsoft.ch> - 2015-09-09 23:49 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-10 14:43 -0400
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-10 16:10 -0400
                Re: GA144 use cases Stefan Mauerhofer <smauerhofer@androsoft.ch> - 2015-09-12 03:15 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-12 10:28 -0400
                Re: GA144 use cases Greg <abiforth@gmail.com> - 2015-09-13 13:05 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-13 18:59 -0400
                Re: GA144 use cases Greg <abiforth@gmail.com> - 2015-09-13 18:42 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-13 22:47 -0400
                Re: GA144 use cases Greg <abiforth@gmail.com> - 2015-09-13 21:24 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-14 02:00 -0400
                Re: GA144 use cases borota@gmail.com - 2015-09-14 08:35 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-14 12:06 -0400
                Re: GA144 use cases borota@gmail.com - 2015-09-14 09:33 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-14 13:25 -0400
                Re: GA144 use cases Greg <borota@gmail.com> - 2015-09-14 14:17 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-14 18:12 -0400
                Re: GA144 use cases Greg <schmegner@gmail.com> - 2015-09-14 18:15 -0700
                Re: GA144 use cases rickman <gnuarm@gmail.com> - 2015-09-14 22:16 -0400
                Re: GA144 use cases Greg <borota@gmail.com> - 2015-09-18 14:50 -0700
                Re: GA144 use cases Jason Damisch <jasondamisch@yahoo.com> - 2015-09-18 15:11 -0700
                Re: GA144 use cases Greg <borota@gmail.com> - 2015-09-19 05:32 -0700
                Re: GA144 use cases Dennis Ruffer <daruffer@gmail.com> - 2015-09-19 08:39 -0700
                Re: GA144 use cases Greg <borota@gmail.com> - 2015-09-20 19:03 -0700
                Re: GA144 use cases Dennis Ruffer <daruffer@gmail.com> - 2015-09-21 06:44 -0700
                Re: GA144 use cases Dennis Ruffer <daruffer@gmail.com> - 2015-09-22 13:10 -0700
                Re: GA144 use cases Mark Wills <markwills1970@gmail.com> - 2015-09-18 16:18 -0700
                Re: GA144 use cases schmegner@gmail.com - 2015-09-14 18:21 -0700

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