Re: parList implementation question

20 Dec 2009

      Well, I finally put in place 6.12.1 and read the documentation for
Control.Parallel.Strategies.  All of my code for the application described
below uses Done, demanding, sparking, (>|), and (>||) which are deprecated
and which is what I used.  Additionally, I need to understand Eval first
to change my code.

No point in responding until I determine what this means.

Thanks nevertheless,
- Marcus

Marcus D. Gabriel wrote:
...
Denis Bueno wrote:
...
On Fri, Dec 18, 2009 at 11:31, Marcus D. Gabriel  wrote:
...
than parList via parMap.  For example, in one experiment, parMap
with parList run at 0.81 the time of the serial solution whereas
forceParMap with forceParList run at 0.58 the time of the serial
solution.  This is to say, forceParList completed in 0.72 the
time of parList.  So,
I don't know your application, so it's hard to interpret your numbers.
Are you sure those measurements are statistically significant?
The particular example that I gave was a straightforward
searchDepthFirst(1) algorithm. To parallelise it, I choose the
initial, simple approach to determine the first list of successor
nodes from an initial node and use parMap to apply the serial
algorithm searchDepthFirst to this list and then reduce (concat)
the list.
With some RTS tuning and using a dedicated dual-core system, I was
able for the problem above to reproduce the numbers that I cite
above consistently to within about plus or minus a factor of 0.01.
I have played with variations of this class of problem but not
generally compared parList with forceParList across a broader class
of problems.
I like your question above.  It helped me formulate this question:
Is what I observed above significant or random?  I hope it is not
random.
I guess the deeper question is how does one determine with
confidence that
parallised serial algorithm + startegy1 works for problem class1
and
parallised serial algorithm + startegy2 works for problem class2
where both are better than the serial case for their respective
class of problems across a given range of operating environments,
e.g., -N2 to -N8 for 2 to 8 cores.
- Marcus
(1) "Algorithms, A Functional Programming Approach" by Fethi Rabhi
and Guy Laplame.  ISBN 0201-59604-0.
-- 
  Marcus D. Gabriel, Ph.D.                         Saint Louis, FRANCE
  http://www.marcus.gabriel.name            mailto:marcus@gabriel.name
  Tel: +33.3.89.69.05.06                   Portable: +33.6.34.56.07.75