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June 2008

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Subject:
From:
Sean Luke <[log in to unmask]>
Reply To:
ECJ Evolutionary Computation Toolkit <[log in to unmask]>
Date:
Mon, 2 Jun 2008 16:22:17 -0400
Content-Type:
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There are no dependencies between breedthreads and evalthreads.  It's  
actually quite simple if you're doing plain generational evolution,  
it's roughly:

Eval:
	For each thread
		Create a Problem for that thread
		Fork a thread to do PopSize/NumThreads evals
Breed:
	For each thread
		Create a BreedingPipeline for that thread
		Fork a thread to do Popsize/NumThreads new individuals

There's no locking in ECJ's basic eval or breed facilities (which is  
why we need multiple RNGs).  Most performance failures in the  
threading are due to (1) GC and (2) memory access with a poor memory  
controller, if not (3) a synchronization you put in there but forgot  
about :-).  My guess is #2 -- it bites us in MASON too.  Basically  
although the cores can go full-blast, if you're doing lots of fetches  
from cold memory (as ECJ is doing constantly -- it does scans across  
populations), there's only *one* memory and cache controller on the  
machine and that becomes the bottleneck.

That being said, ECJ will get about 40% improvement on a two-core  
Intel chip.   For example, when I run ecsuite with 1000 individuals,  
here are some rough wall-clock times I get on my Macbook Pro:

	1 breed   1 eval	24 secs
	2 breed   1 eval	21 secs
	1 breed   2 eval	19 secs
	2 breed   2 eval	17 secs

Note that eval gives you a bigger boost than breed in this example.

You might try fooling with the GC parameters (-Xmx and -Xms for  
setting, -verbose:gc for testing), though it probably won't be a big  
deal for you.

Sean

On Jun 2, 2008, at 10:16 AM, Denis Robilliard wrote:

> Hi,
>
> I just performed some experiences with the "breedthreads" and  
> "evalthreads" parameters on the tutorial regression problem. On a  
> dual core machine, I observed that the performance increases  
> (computing time roughly divided by 2) when breedthreads = 2 &  
> evalthreads=1,  but there is no gain when breedthreads = 1 &  
> evalthreads=2 . However the stat file shows that most of the  
> running time is spent for evaluation (as expected). Is there some  
> dependencies between breedthreads and evalthreads values ?
>
> -- 
> Denis Robilliard
> L.I.L.
> Universit du Littoral
> 50 rue F. Buisson
> 62100 Calais
> France

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