GPU wrong results
显示 更早的评论
Hello, I just started using GPU with matlab and I get some strange results. I run the following code
a = rand(2^10,2^10,'single');
G = gpuArray(a);
F = fft2(G);
err = isequal(gather(G), a)
Normally the value o 'err' should be 1, but in this case is not. If you call another function, e.g. instead of fft2 call atan, then the value of err is 1. Do you have any idea why this happens?
The GPU model is "GeForce GTX 580" and the matlab version is 2010b.
Thanks a lot.
7 个评论
Jason Ross
2011-10-27
What is the value of err that you get?
Georgios
2011-10-27
Edric Ellis
2011-10-31
This is definitely unexpected, and you're right - there should be no difference between 'a' and 'gather(G)' for this case, and I don't see this problem on my C1060 card using R2011b. (As Jan points out, if you're doing computation on the GPU, then the values might diverge very slightly due to different algorithms being used).
Have you tried different NVIDIA drivers?
Ben Tordoff
2011-10-31
Hi Georgios, I've been trying to reproduce this to no avail. Unfortunately I don't have access to a GTX 580, but I've tested running your code-snippet 1000 times in R2010b on each of: Quadro 600, GTX 460, GTX 480, Tesla C1060 and Tesla C2070. I can't get the test to fail even once on any of them.
What OS are you using? If you're not using the latest NVIDIA drivers, upgrading those is worth a try (as Edric suggests).
Jan
2011-10-31
@Ben: I'm impressed by your GPU pool.
It seems to be obvious (we call such terms Wischi-Waschi in German, a kind of "limited scientfical power") that the GPU-processing is prone to drive problems and I assume is sensitve to overheating of the board also.
Is there a test-suite such that I can check my GPU before I trust the results e.g. for clinical decision making?
Walter Roberson
2011-10-31
It appears that the German Wischi-Waschi came down to English as "wishy-washy". I had no idea of the origin of the English term before.
Georgios
2011-10-31
回答（2 个）
Jan
2011-10-27
Do you expect absolutely equal results without rounding errors? This will happen as an exception only. Please check:
g = gather(G);
disp(max(abs(g(:) - a(:))));
4 个评论
Georgios
2011-10-27
Jan
2011-10-27
Now I see: The F=fft2(G) is not involved in the comparison, it is just to stress the graphics board. This is strange.
Jan
2011-10-31
A large FFT2 produces some heat on the GPU. Does this influence the local memory such that your data are simply corrupted?
Georgios
2011-10-31
Thomas
2011-11-2
Georgios, I ran it on our GPU pool
gpuDevice
tic ()
a = rand(2^10,2^10,'single');
G = gpuArray(a);
F = fft2(G);
err = isequal(gather(G), a)
toc ();
The output was ans =
parallel.gpu.CUDADevice handle
Package: parallel.gpu
Properties:
Name: 'Tesla M2070-Q'
Index: 1
ComputeCapability: '2.0'
SupportsDouble: 1
DriverVersion: 4.1000
MaxThreadsPerBlock: 1024
MaxShmemPerBlock: 49152
MaxThreadBlockSize: [1024 1024 64]
MaxGridSize: [65535 65535]
SIMDWidth: 32
TotalMemory: 5.6366e+09
FreeMemory: 5.5281e+09
MultiprocessorCount: 14
ClockRateKHz: 1147000
ComputeMode: 'Default'
GPUOverlapsTransfers: 1
KernelExecutionTimeout: 0
CanMapHostMemory: 1
DeviceSupported: 1
DeviceSelected: 1
err =
1
Elapsed time is 0.054194 seconds.
I am getting an err = 1 output..
类别
在 帮助中心 和 File Exchange 中查找有关 GPU Computing in MATLAB 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
