Trying to use 'parfor', but it is very slow
1 view (last 30 days)
Show older comments
Hello, I am trying to use parfor as below.
-------------------------
parpool(2)
A=zeros(10,10);
for iX=1:10
parfor iY=1:10
A(iY,:)=rand(1,10);
end
end
----------------------
However, the case of replacing the 'parfor' with 'for' is 20 times faster. Above code is simplified version of what I'm using. In my real case, 'parfor' should be inside 'for'. Is this a problem?
Could anyone explain why?
Thank you in advance.
1 Comment
Adam
on 20 Feb 2015
As per Doug's answer since you also only have 2 cores (or are only using 2 cores) you will have to be doing more work to make the parfor setup worthwhile than if you had e.g. 8 cores because the absolute maximum theoretical speedup factor will only be 2 and realistically it is obviously lower than that even when running optimally.
Answers (1)
Doug
on 20 Feb 2015
You're not doing enough work in the parfor loop. Since there is an overhead associated with parfor, you have to perform enough operations in the loop to make it worthwhile. Also, it's better if your parfor is not inside a for loop, since otherwise you incur the parfor startup overhead each iteration. You may want to try an example such as http://www.mathworks.com/help/distcomp/examples/simple-benchmarking-of-parfor-using-blackjack.html .
0 Comments
See Also
Categories
Find more on Parallel for-Loops (parfor) in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!