CODEWITHSUNDEEP
matlabperformancegpu
Liz Salander
Liz Salander

Reputation: 321

GPU timing in Matlab

I am using a GeForce GT 720 to do some basic calculations in Matlab.

I am simply doing matrix multiplication:

A = rand(3000,3000);     % Define array using CPU
tic;                     % Start clock
Agpu = gpuArray(A);      % Transfer data to GPU
Bgpu = Agpu*Agpu;        % Perform computation on GPU
time = toc;              % Stop clock

In this code, my clock is timing the data transfer to the GPU and matrix multiplication on the GPU, and I get time ~ 4 seconds. I suspect that the data transfer is taking much more time than the multiplication, so I isolate it with my timer: 

A = rand(3000,3000);     % Define array using CPU
tic;                     % Start clock
Agpu = gpuArray(A);      % Transfer data to GPU
time = toc;              % Stop clock
Bgpu = Agpu*Agpu;        % Perform computation on GPU

and indeed it takes ~ 4 seconds. However, if I comment the last line of the code, so that no multiplicaiton is done, my code speeds up to ~0.02 seconds.

Does performing a computation with the GPU after transferring data to the GPU alter the speed of the data transfer?

Upvotes: 2

Views: 236

Answers (1)

Edric
Edric

Reputation: 25140

I don't see this behaviour at all (R2017b, Tesla K20c) - for me, either way, the transfer takes 0.012 seconds. Note that if you're running this in a fresh MATLAB session each time, the very first time you run anything at all on the GPU takes a few seconds - perhaps that accounts for the 4 seconds?

In general, use gputimeit to time stuff on the GPU to ensure you don't see strange results from the asynchronous nature of some GPU operations.

Upvotes: 2

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