Unspecifiec launch failure on CUDA_SAFE_CALL(cudaThreadSynchronize())

Accelerated Computing CUDA CUDA Programming and Performance
1

Hello,

I’m trying to convert a very slow serial program to GPU. Problem is, I get the “Unspecified launch failure” error message every time I run it. The line that the CUDA error points to is

CUDA_SAFE_CALL( cudaThreadSynchronize() );

which I have inserted directly after my call to the kernel. I am really perplexed and hoping that someone can help. I’ve compiled and run a number of other codes, so I think I’ve got my system properly configured.

The command line is (from Properties->Configuration Properties->CUDA Runtime API->Command Line):

echo “C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v3.2\bin\nvcc.exe” -gencode=arch=compute_20,code="sm_20,compute_20" -gencode=arch=compute_20,code="sm_20,compute_20" --machine 32 -ccbin “C:\Program Files\Microsoft Visual Studio 9.0\VC\bin” -Xcompiler “/EHsc /W3 /nologo /O2 /Zi /MT " -I"C:\Documents and Settings\All Users\Application Data\NVIDIA Corporation\NVIDIA GPU Computing SDK 3.2\C\common\inc” -I"C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v3.2\include" -maxrregcount=32 --compile -o “Debug/Image_Dist.vcproj.obj” Image_Dist.vcproj
“C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v3.2\bin\nvcc.exe” -gencode=arch=compute_20,code="sm_20,compute_20" -gencode=arch=compute_20,code="sm_20,compute_20" --machine 32 -ccbin “C:\Program Files\Microsoft Visual Studio 9.0\VC\bin” -Xcompiler “/EHsc /W3 /nologo /O2 /Zi /MT " -I"C:\Documents and Settings\All Users\Application Data\NVIDIA Corporation\NVIDIA GPU Computing SDK 3.2\C\common\inc” -I"C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v3.2\include" -maxrregcount=32 --compile -o “Debug/Image_Dist.vcproj.obj” “c:\Tim\Image_Dist\Image_Dist.vcproj”

I am using Visual C++ 2008 Express Edition with the CUDA 3.2 SDK and a GTX 570 card.

Here’s the relevant bit of host code. pos and dist are float** and num_zero, x, y, and len are ints

    // Allocate matrices in device memory
    size_t pitch;
int* dzeros;
cudaMalloc((void**)&dzeros,	num_zero * sizeof(int));
float* dpos;
cudaMallocPitch((void**)&dpos,&pitch,10 * sizeof(float),len);
float* ddist;
cudaMallocPitch((void**)&ddist,&pitch,(len+2)*sizeof(float),num_zero);

// Copy matrices from host memory to device memory
cudaMemcpy(dzeros,thezeros,num_zero*sizeof(int),cudaMemcpyHostToDevice);
cudaMemcpy2D(dpos,pitch,pos,pitch,10*sizeof(float),len,cudaMemcpyHostToDevice);
cudaMemcpy2D(ddist,pitch,dist,pitch,(len+2)*sizeof(float),num_zero,cudaMemcpyHostToDevice);

// Send the task out
dim3 threads(1, 1);
    dim3 grid(x / threads.x, y / threads.y);
cudaError_t cudastat;

computedist<<<grid,threads>>>(dzeros,dpos,ddist,num_zero,x,len,pitch);
CUDA_SAFE_CALL( cudaThreadSynchronize() );

Here’s the device code:

global void computedist(int* dzeros,float* dpos,float* ddist,int num_zero,int x,int len,size_t pitch){
// Block index
int bx = blockIdx.x;
int by = blockIdx.y;
// Thread index
int tx = threadIdx.x;
int ty = threadIdx.y;
// Block Dimension
int dx = blockDim.x;
int dy = blockDim.y;

int i = bx*dx+tx;
int j = by*dy+ty;

int index = i*x+j;
int theind;

for(theind=0;theind<num_zero;theind++)
	if(dzeros[theind]==index)
		break;

// Pointers to matrix locations
float* location;
float* r;
float* c;

location = (float*)((char*)ddist + theind*pitch);
*location = i;
location = (float*)((char*)ddist + theind*pitch) + 1;
*location = j;
for(int ind=0;ind<len;ind++){
	location = (float*)((char*)ddist + theind*pitch) + ind+2;
	r = (float*)((char*)dpos + ind*pitch) + 6;
	c = (float*)((char*)dpos + ind*pitch) + 5;
	*location = sqrt((i-*r)*(i-*r)+(j-*c)*(j-*c));
}

}

2

According to my experience in 99% of cases that means that your kernel is doing something wrong, like access violation for example. In this case the next cuda call signales unspecified error.
I recommend you first run it under the nsight parallel debugger with memory checking enabled, then if that doesn’t point you to the problem start commenting out parts of your kernel until the problem goes away, keep commenting out piece by piece until you isolate the problem to a specific line.

3

disclaimer: I’m a total newbie

If you look at the definition of the CUDA_SAFE_CALL macro it actually calls cudaThreadSynchronize()
http://forums.nvidia.com/index.php?showtopic=66907

So maybe it has something to do with it being called again?

4

Any errors reported by cudaThreadSynchronize() are delayed errors that were caused by a previous kernel launch (or any other async CUDA call).

5

I’m guessing ( because I gave up trying to understand your code) that you’ve got an access violation in your kernel.

Your code is WAY too complicated for what it appears (?) to be doing.
Why all the pointer casting … float ->char->float ?
Why are you even using pointers for this?

Also, in general, it’s a lot easier to use flattened 1-D rather than 2-D.

6

I’ve kind of abandoned this problem. I was just using it to get familiar with CUDA before I moved on to the real thing that I’m interested in. As for what was causing the error, it seems to have been some combination of writing to device memory poorly and trying to pass things to the device that were too large. And looking at it now, the code is a mess. I tried to convert some MATLAB code I had, and it ended up pretty lousy. So if anyone is looking to solve a similar problem, just disregard my code.