Batch sounds slower than interactive parallel jobs

2013 7 9
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Hi !
I use Matlab 7.10.0 and Parallel Toolbox on a 8 cores blade.
Issuing that command :
tic;job=batch('birthdayscript','matlabpool',4);wait(job);ovrHead=toc;
I obtain ovrHead = 10.42 seconds
Issuing that command :
matlabpool open 4;tic;p = prunbirthday(2e4, 30), ovrHead=toc;matlabpool close
I obtain ovrHead = 1.39 seconds
May I ask you why batch method is so ineffective ?
Sylvain
PS : here the code of birthdayscript :
numtrials = 2e4;
groupsize = 30;
% Preallocate some memory for the matches
matches = zeros(1, numtrials);
parfor trial = 1:numtrials
% Run a simulation for a group
matches(trial) = birthday(groupsize);
end
% Probability is the sum of matches divided by number of trials
prob = sum(matches)/numtrials;

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Sean de Wolski
Sean de Wolski 2013-7-9
编辑：Sean de Wolski 2013-7-9

1 个投票

batch is opening its own MATLAB pool of four workers so this is included in the timing of the first snippet and not the second.

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Sylvain Rousseau
Sylvain Rousseau 2013-7-10
编辑：Sylvain Rousseau 2013-7-10

0 个投票

Dear Sean,
Thanks for your answer.
That's what I thought at first sight, but the task overhead is the same when I move the tic after the batch() statement :
job=batch('birthdayscript','matlabpool',4);tic;wait(job);ovrHead=toc;
Here again, I obtain ovrHead = 10.42 seconds
Moreover, if I increase workers number up to seven (findResource gives a clusterSize of 8) , the overhead stays the same although I'am the only user of the computer.
Cheers.
sylvain

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