why is parfor slower than for?

Question

Celso Cruz 2013-5-9

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/75166-why-is-parfor-slower-than-for

In this case, t_parfor is higher than t_for.

N = 100000;
x=zeros(1,N);
tic;
for i = 1 : N
    x(i)=rand();
end
t_for = toc;
tic;
parfor i = 1 : N
    x(i)=rand();
end
t_parfor = toc;
t_for
t_parfor

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Answer 1

Sean de Wolski 2013-5-9

4
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/75166-why-is-parfor-slower-than-for#answer_84875

First, do you have a matlabpool open? If no matlabpool is open then the parfor loop will not be run in parallel anyway.

Here the data transfer and communication overhead cost more than the computation. parfor will do the most good when the data transfer is low and the calculation time is high.

(And I assume you are aware of: x = rand(N,1) % ;) )