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Re: [Bug-apl] apl computer

From: Xiao-Yong Jin
Subject: Re: [Bug-apl] apl computer
Date: Fri, 26 Aug 2016 15:57:36 -0500

Of course.  Simple scalar functions would be the worst to parallelize.
We always need a large amount of operations per thread to be worthwhile.
Something like the following might be a good thing to start
   ⌹⍤2 X
where (LargeNumber = ×/¯2↓⍴X) ∧ 2<⍴⍴X
To support general function instead of builtins the code would need to analyze 
the data dependencies, which I believe is impossible in APL because of ⍎ can’t 
be done without execute it, but supporting a subset seems good enough.  Looking 
at data parallel Haskell, and you know it’s a really hard problem.

I wish there will be an array language that could hide all the details of 

There are some efforts in bringing SIMD type executions to array languages but 
in my opinion these are just not enough, as our central processors having more 
and more fast cores/threads.  (Once there was a time when APL was wonderful in 
utilizing computing powers, but it’s long gone.)

> On Aug 26, 2016, at 2:34 PM, Juergen Sauermann <address@hidden> wrote:
> Hi,
> maybe, maybe not.
> Our earlier measurements on an 80-core machine indicated that
> the way how the cores connect to the memories seems to determine the
> parallel performance that can be achieved in GNU APL.
> One can easily prove that for sufficiently large APL arrays (of arbitrary 
> rank) all scalar APL
> functions must scale linearly with N on a N-processor PRAM.
> See http://link.springer.com/chapter/10.1007%2F978-3-642-61012-7_11 (in 
> German).
> One can also show that on the 80-core machine that we used, the performance 
> stops increasing
> at fairly low N (around 10) even for very large arrays.
> Which means that either the GNU APL parallel implementation of scalar 
> functions is wrong or
> that the 80-core machine we used is performance-wise not even near the PRAM 
> model. My best
> guess is the latter.
> /// Jürgen
> On 08/26/2016 08:41 PM, Xiao-Yong Jin wrote:
>>> On Aug 26, 2016, at 1:12 PM, address@hidden
>>>  wrote:
>>> finally a computer just perfect for gnuapl
>>> http://thehackernews.com/2016/08/powerful-multicore-processor.html
>> Now is the perfect time to invest your time and effort in improving parallel 
>> efficiency in gnu-apl.

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