Parfor loop with 4 workers is more than 4 times faster than the for loop, how is it possible?

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Pilar Julieta Tagliero 2021-6-25

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https://ww2.mathworks.cn/matlabcentral/answers/865325-parfor-loop-with-4-workers-is-more-than-4-times-faster-than-the-for-loop-how-is-it-possible

回答： Edric Ellis 2021-6-28

Hello,

I have a code that contains a for loop inside a while loop.

When I change the for to parfor, the elapsed time I get is divided by "n" times, being "n" higher than 4 for some input data.

How is it possible if my pool has 4 workers? I'm using tic/toc functions to measure the time.

Thank you!

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Answer 1

Edric Ellis 2021-6-28

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https://ww2.mathworks.cn/matlabcentral/answers/865325-parfor-loop-with-4-workers-is-more-than-4-times-faster-than-the-for-loop-how-is-it-possible#answer_734965

Without seeing some code that demonstrates this, we can only speculate. One possibility is that the code transformations required to make a parfor loop execute have ended up being more efficient. Is your parfor loop currently in a script? (There are different MATLAB-level optimisations available to scripts and functions - but the body of a parfor loop always has to execute in the same was as if it was placed inside a function).