Why GPU performance is worse than CPU for this code?

3 views (last 30 days)
King Fisher
King Fisher on 27 Nov 2011
clear all
close all
tic
t=9999;
X = rand( t, 'single' );
G = gpuArray( X );
isequal( gather( G ), X ) % returns true
classUnderlying( G ) % returns 'single'
G2 = G .* G
toc
tic
X = rand( t, 'single' );
G1 = X;
G3 = G1 .* G1 ;
toc
The execution time of GPU is less than CPu i5. Would anybody answer it?
  1 Comment
Jan
Jan on 27 Nov 2011
About "clear all" see: http://www.mathworks.com/matlabcentral/answers/16484-good-programming-practice#answer_22301
Please decide, if the "GPU performance is worse than CPU", or if "the execution time of GPU is less than CPU".

Sign in to comment.

Sign in to answer this question.

Accepted Answer

Walter Roberson
Walter Roberson on 27 Nov 2011
There is a lot of overhead for sending data to a GPU. It is only faster for sufficiently big matrices.
Also, in the first one you are including the "isequal" and the "classUnderlying" in the timing, neither of which is needed for the computation. It is not fair to time different sets of activities.

More Answers (2)

Jan
Jan on 27 Nov 2011
Please try this:
X = rand(1e3, 1e3, 'single' );
G = gpuArray( X );
G2 = G;
tic
for i = 1:100
G2 = G2 .* G;
end
toc
tic
G = X;
G2 = X;
for i = 1:100
G2 = G2 .* G;
end
toc
cdarling
cdarling on 19 Feb 2012
there is a possibility that your GPU supports parallel.gpu.GPUArray.rand(), and it would be much faster if you construct random numbers within GPU, instead of generate and copy them into GPU

Categories

Find more on GPU Computing in Help Center and File Exchange

Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!