CUDA:两个数字相加给出错误答案

Question

这是程序

#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;
}

这是我编译它的方法

$ nvcc -o test test.cu

这是我的输出

1

这是 deviceQuery 的输出

./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

Answer 1

CUDA 6.5 默认编译为 cc2.0 目标。您的 GeForce 8400GS 是 cc1.1 设备。因此，以这种方式编译的内核将无法启动，并且您没有 proper cuda error checking在你的代码中(这会给你一个问题的指示)。

如果您在编译时指定了正确的 arch 开关，您的代码应该可以正常运行:

nvcc -arch=sm_11 -o test test.cu

将显示一条警告消息，指出 sm_11 已弃用，但它仍应正确编译您的代码。