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Re: GA144 use cases

From anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups comp.lang.forth
Subject Re: GA144 use cases
Date 2015-09-05 15:10 +0000
Organization Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID <2015Sep5.171017@mips.complang.tuwien.ac.at> (permalink)
References (7 earlier) <msa991$ga4$1@dont-email.me> <877fo7gqvv.fsf@jester.gateway.sonic.net> <msal0b$udo$1@dont-email.me> <2015Sep4.102450@mips.complang.tuwien.ac.at> <msc53k$en6$1@dont-email.me>

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Bernd Paysan <bernd.paysan@gmx.de> writes:
>Anton Ertl wrote:
>
>> Bernd Paysan <bernd.paysan@gmx.de> writes:
>>>Paul Rubin wrote:
>>>> In the uncontended case you check a futex in user space and proceed if
>>>> there's something to do, or yield to the kernel if there's nothing to
>>>> do.  There's only IPC overhead if there's contention in which case you
>>>> have to make a system call.
>>>
>>>Unfortunately, the contention is the rule, and the uncontented case the
>>>exception.  The problem of asynchronous tasks is that either the producer
>>>or the consumer waits, and that's the contented case.
>> 
>> No, the contended case is when both want to change the status at the
>> same time.
>
>No, that's not a resource lock, that's a wakeup signal.

Only one thread is active, so there can be no contention.  You are
thinking about something that is not contention.

>>>  So either the producer
>>>has to tell the consumer "good morning, time to wake up, I've some new
>>>data for you", or the consumer says "good afternoon, producer, stop
>>>napping, and give me another chunk of data".
>> 
>> Sounds to me like you have a GA144-like model with little or no
>> buffering.  Then of course you will have little parallelism; after
>> all, the GA144 was designed to let many of the cores sleep most of the
>> time.
>
>When the consumers are faster than the produces, your buffers won't fill up.  
>You can introduce arbitrary delays to keep your buffers filled, but this 
>also reduces performance, as other tasks will be waiting much longer for the 
>results.

If the consumers are faster than the producers, run the producers on
more cores than the consumers.  If you have only one producer, and
that is sequential, and the consumers combined are still faster than
the producer, you have a parallelism of <2.  You can still reduce the
wakeup overhead by only sending wakeup signals when the producer has
produced enough (and stored it in a buffer) that the wakeup overhead
is small compared to the processing time.  Yes, this increases
latency, so it's a balance of efficiency vs. latency; you can bound
the increase in latency by waking the consumer some fixed time after
the producer has started producing.

>And yes, I've a model in mind, where more compute cores are sleeping than 
>working; with a x64-style implementation, you would use SMT for that, not 
>multiple cores.

If there are not enough active threads for all the cores, the only
reason to use SMT is to conserve energy or because communication is
cheaper (the shared cache is L1 instead of L3).  But if you are
interested in performance, I expect that, running two threads on two
otherwise idle cores usually gives better performance than running
them in the same core, even if they communicate.  Sure, there is the
PAUSE instruction for slowing a waiting thread down, but even with
that, i expect that situation where SMT performs better than two cores
are not very common.

>And buffering reduces performance, as it requires way more actual 
>parallelism.

Buffering also enables parallelism.  E.g., with a conventional screen
and with vertical synchronization to avoid tearing, double buffering
means that rendering has to wait for the vsync, while with tripple
buffering there can be rendering all the time.

Anyway, yes, you were talking of having lots of little tasks, which
sounds like having lots of parallelism to me.  Then you switch to a
hardly-parallel problem of one sequential producer and consumers that
need little CPU.  Of course these different kinds of problems need
different solutions.

>> So don't use the OS in the normal case.
>
>Anton, that's the entire point of suggesting that the wake/sleep IPC should 
>be done in hardware.

Well, Intel tried that kind of thing in the iAPX 432 and in the 80286
protected mode and the hardware operations (task gates) were slow.  A
context switch is slow whether it is done in hardware or in software.

You may be dreaming of hardware that has, say, dozens sets of
process/thread states per core, most of which are sleeping most of the
time, and that can put themselves to sleep cheaply, and be woken up
cheaply, but you have to make a really good case for that to get it
included in hardware.  Is your model of lots of small tasks with
little parallelism overall really that relevant?

- 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/

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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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