CODEWITHSUNDEEP
ccudanvidia
skwalker
skwalker

Reputation: 329

CUDA: Addition of two numbers giving wrong answer

Here is the program 

#include <stdio.h>
#include <cuda.h>
#include <cuda_runtime.h>
   #include <device_launch_parameters.h>

   __global__ void Addition(int *a,int *b,int *c)
   {
      *c = *a + *b;
}
int main()
{
  int a,b,c;
  int *dev_a,*dev_b,*dev_c;
  int size = sizeof(int);

  cudaMalloc((void**)&dev_a, size);
  cudaMalloc((void**)&dev_b, size);
  cudaMalloc((void**)&dev_c, size);

  a=5,b=6;

  cudaMemcpy(dev_a, &a,sizeof(int), cudaMemcpyHostToDevice);  
  cudaMemcpy(dev_b, &b,sizeof(int), cudaMemcpyHostToDevice);  

  Addition<<< 1,1 >>>(dev_a,dev_b,dev_c);
  cudaMemcpy(&c, dev_c,size, cudaMemcpyDeviceToHost);

   cudaFree(&dev_a);
   cudaFree(&dev_b);
   cudaFree(&dev_c);

   printf("%d\n", c);
   return 0;
}

Here is how i compiled it

$ nvcc -o test test.cu

Here is my output

1

Here is the output of deviceQuery

./deviceQuery Starting...

CUDA Device Query (Runtime API) version (CUDART static linking)

Detected 1 CUDA Capable device(s)

Device 0: "GeForce 8400 GS"
CUDA Driver Version / Runtime Version          6.5 / 6.5
CUDA Capability Major/Minor version number:    1.1
Total amount of global memory:                 511 MBytes (536150016 bytes)
( 1) Multiprocessors, (  8) CUDA Cores/MP:     8 CUDA Cores
GPU Clock rate:                                1350 MHz (1.35 GHz)
Memory Clock rate:                             400 Mhz
Memory Bus Width:                              64-bit
Maximum Texture Dimension Size (x,y,z)         1D=(8192), 2D=(65536, 32768), 3D=(2048, 2048, 2048)
Maximum Layered 1D Texture Size, (num) layers  1D=(8192), 512 layers
Maximum Layered 2D Texture Size, (num) layers  2D=(8192, 8192), 512 layers
Total amount of constant memory:               65536 bytes
Total amount of shared memory per block:       16384 bytes
Total number of registers available per block: 8192
Warp size:                                     32
Maximum number of threads per multiprocessor:  768
Maximum number of threads per block:           512
Max dimension size of a thread block (x,y,z): (512, 512, 64)
Max dimension size of a grid size    (x,y,z): (65535, 65535, 1)
Maximum memory pitch:                          2147483647 bytes
Texture alignment:                             256 bytes
Concurrent copy and kernel execution:          No with 0 copy engine(s)
Run time limit on kernels:                     Yes
Integrated GPU sharing Host Memory:            No
Support host page-locked memory mapping:       Yes
Alignment requirement for Surfaces:            Yes
Device has ECC support:                        Disabled
Device supports Unified Addressing (UVA):      No
Device PCI Bus ID / PCI location ID:           1 / 0
Compute Mode:
< Default (multiple host threads can use ::cudaSetDevice() with device simultaneously) >

deviceQuery, CUDA Driver = CUDART, CUDA Driver Version = 6.5, CUDA Runtime     Version = 6.5, NumDevs = 1, Device0 = GeForce 8400 GS
Result = PASS

Upvotes: 2

Views: 883

Answers (1)

Robert Crovella
Robert Crovella

Reputation: 151954

CUDA 6.5 compiles for a cc2.0 target by default. Your GeForce 8400GS is a cc1.1 device. So your kernels compiled that way will not launch, and you don't have proper cuda error checking in your code (which would have given you an indication of the problem).

If you specify a proper arch switch when compiling, your code should run properly:

nvcc -arch=sm_11 -o test test.cu

A warning message will be displayed that sm_11 is deprecated, but it should still compile your code properly.

Upvotes: 4

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