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From: Anatoly Chernyshev <achernyshev@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Multicore problem
Date: Tue, 9 Mar 2010 10:48:34 -0800 (PST)
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> Perhaps the two tasks/cores are competing for data-cache space, and
> causing more cache misses than if a single task/core is active?
>
> How large is your 3D array, compared to the cache?

Right now it is small, 23 Mb, for the purposes of algorithm honing.
2Mb L2 cache. In perspective the array could be 4-8 Gb (not for my
current machine, of course).

> If this is the problem, you could try to divide the whole problem into
> slices so that each slice processes a part of the 3D array that *can*
> fit in the cache, but can also be processed in parallel by two
> tasks/cores. Not knowing what your processing actually does I can't say
> more about how to slice the problem.

Each task begins in the cell of its designated area of array, and then
does a Markov walk all around the place using the cell pointers.