Cuda By Example Questions about some of the examples

Accelerated Computing CUDA CUDA Programming and Performance
#1

Hello all,

I finished reading Cuda By Example recently and there are a couple of things that I need clarification on.

  1. One of the examples allocates Shared memory for the block inside of the kernel:

global void histo_kernel( unsigned char *buffer,long size,unsigned int *histo )
{
shared unsigned int temp[256];
.
some other code
.
}

Why do we define the shared memory there inside of the kernel. Isn’t the shared memory being allocated multiple times for each of the threads in a particular block?

  1. The Heat 2d example from chapter 7 is taking a really long time for each render. Somewhere between 350ms - 500ms depending on the arc I’m using (1.0, 1.3, 2.0). Is this time normal for this example.

Okay, this next one isn’t a Cuda By Example question, but I’m trying to use curand to generate some random numbers on the device. However the numbers are not completely random. I have a lot of copies of numbers. For example it would look something like this. {5642, 12314, 8469, 12314,8964302, 5642 96341}

I’m using the same major parts of the code that is outlined in the CURAND_Library.pdf

Thanks for your time

#2

No. I think that the memory is allocated only once for each block.

#3

Shared memory is by definition always allocated per block.

Can you show the code you use to setup and call CURAND? Results like you are seeing sometimes result from a failure to initialize the curandState struct before using it.

#4

This is the basic outline for curand in my code:

#define Population_Size 100

#define Dim 20

struct Chrome{

int fitness[Dim];

};

global void SeedSet(curandState *state, unsigned long seed)

{

int id = threadIdx.x + blockIdx.x * Dim;

curand_init(seed, id, 0, &state[id]);

}

global void Fitnesseval (Chrome *dPop, curandState *state)

{

curandState localState = state[Dim*blockIdx.x + threadIdx.x];//setting state for RNG

dPop[blockIdx.x].fitness[threadIdx.x] = curand(&localState);

}

int main(void)

{ Chrome hPop[Population_Size];

Chrome *dPop;

cudaMalloc( (void**)&dPop,sizeof(Chrome)*Population_Size);

curandState *devStates;

cudaMalloc((void **)&devStates, Population_Size * Dim *sizeof(curandState));

SeedSet<<<Population_Size, Dim>>>(devStates, time(NULL));

Fitnesseval<<<Population_Size, Dim>>>(dPop, devStates);

cudaMemcpy( &hPop, dPop,sizeof(Chrome)*Population_Size,cudaMemcpyDeviceToHost);

return 0;

}

Edit: __________________________

Now that I have ran this little example it works just fine. I should go take a look at my original code, I must have screw up somewhere.

Thanks anyways!