How to resolve warning message about broadcast variable while using 'parfor'?
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Atanu
il 14 Lug 2024 alle 21:29
Commentato: Atanu
il 16 Lug 2024 alle 15:54
males = {'animal1', 'animal2', 'animal3'};
treatmentGrps = {'T1', 'T2', 'T3'};
nrows = size(featureLists, 1);
ncols = size(featureLists, 2);
featureLists = cell(nrows, ncols);
parfor grp = 1:nrows
tempRow = cell(1, ncols);
for animal = 1:ncols
tempRow{animal} = individualPsychValuesPerSession('approachavoid', ...
treatmentGrps{grp}, males{animal});
end
featureLists(grp, :) = tempRow;
end
When I use 'parfor' like above I get an warning message
The entire array or structure 'males' is a broadcast variable.
This might result in unnecessary communication overhead.
But, when I change 'ncols' to 'numel(males)' like following
for animal = 1:numel(males)
tempRow{animal} = individualPsychValuesPerSession('approachavoid', ...
treatmentGrps{grp}, males{animal});
end
for the inner loop I don't get any warning.
Can someone please explain this behavior of 'parfor'?
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Edric Ellis
il 15 Lug 2024 alle 12:09
I think you should ignore this message in this case. It looks like you really need all the values of males for each iteration of the parfor loop, and that's OK. The message is there to warn about cases where the data is being "accidentally" broadcast.
The fact is that the array males is very small (in terms of bytes), so it should not cause significant overhead. You can check using whos to see the size of the array in the workspace, and also use ticBytes and tocBytes to see how much data is being transferred to run the loop. My bet is that the overall data transfer is not being significantly changed by the size of males.
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Drew
il 14 Lug 2024 alle 21:54
Modificato: Walter Roberson
il 14 Lug 2024 alle 22:44
See https://www.mathworks.com/help/parallel-computing/broadcast-variable.html It includes an example with numel().
If this answer helps you, please remember to accept the answer
2 Commenti
Walter Roberson
il 14 Lug 2024 alle 22:44
It was due to the ending period being interpreted as part of the URL. I have corrected the link.
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