Strange gpu arrayfun behavior

5 vues (au cours des 30 derniers jours)
nealm
nealm le 20 Juil 2018
Commenté : Joss Knight le 26 Juil 2018
I have existing code that works but I'd like to accelerate using the GPU version of arrayfun. However the behavior of GPU arrayfun is difficult to understand. According to the documentation the code within the helper function performs scalar operations on the input gpuArray values. However if I try to write my own scalar values the result is unpredictable. To demonstrate, if I have a helper function that look like:
function outArray = simpleTest(inArray)
outArray = inArray * 3.14159;
end
x = gpuArray(1:4);
y = arrayfun(@simpleTest, x);
y = gather(y)
y =
Columns 1 through 2
0.0000 + 0.0000i 0.0000 + 0.0000i
Columns 3 through 4
0.0000 + 0.0000i 0.0000 + 0.0000i
If I pass the scalar value to the helper function, as shown in the second helper function, it does seem to work:
function outArray = simpleTest2(inArray, scalarValue)
outArray = inArray * scalarValue;
end
y = arrayfun(@simpleTest2, x, 3.14159);
y = gather(y)
y =
3.1416 6.2832 9.4248 12.5664
Reading the documentation, I know that the scalar values in the calling function are expanded (similar to bsxfun) however I have been unable to get that function, or any other function, to work within the helper function. I know I'm missing something here, I would appreciate the help.
I have Matlab R2018a with Parallel Computing Toolbox and Cuda version 9.0 installed.
  5 commentaires
nealm
nealm le 24 Juil 2018
Modifié(e) : nealm le 24 Juil 2018
>> which simpleTest
'simpleTest' not found.
>> which simpleTest2
'simpleTest2' not found.
>>
I placed the simpleTest functions in a script. I also tried calling them from their own files, no difference.
Joss Knight
Joss Knight le 24 Juil 2018
Okay, so the next thing to do is to check and upgrade your driver. What is your device? What is your driver version?
gpuDevice
parallel.internal.gpu.CUDADriverVersion

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nealm
nealm le 25 Juil 2018
Joss/OCDER,
I found the source of the problem. I use my own "startup.m" file (which only has "addpath" commands) that is executed at the beginning of a Matlab start. The directories that have been added during the startup process appear to interfere with the way gpu arrayfun executes.
If I don't use the startup.m file gpu arrayfun works fine. Curiously, if I manually run the contents of startup.m AFTER starting Matlab - gpu arrayfun also works fine.
  6 commentaires
nealm
nealm le 26 Juil 2018
Modifié(e) : nealm le 26 Juil 2018
Assuming the call to mtree wasn't normal, I checked the files in my path and didn't find any file that uses classdef mtree directly. Then after some work I think I found the culprit; In my path I have a class folder "@char" where I've redefined the method str2double to that from a mex file from the file exchange:
I had relabeled the function from str2doubleq to str2double for convenience and have used it for several years without issue. After removing this user version of "str2double" from the @char folder, GPU arrayfun behaves normally in all test cases.
Not sure if this is a bug in Matlab or just poor coding form by me, but I'll stop relabeling matlab functions to my own user functions.
Joss Knight
Joss Knight le 26 Juil 2018
Thanks for the investigation! I'll have a look at why str2double is involved and whether I can reproduce your issue. MTree is used to do static analysis of your arrayfun function for the GPU, and presumably str2double is being used to convert the text of your literal value. It may well be a bug that it's possible to break arrayfun by shadowing this function.

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