就把一个一维数组每个元素做个计算，每个block里放256个thread，blockDim输出出来是(256,1,1)；然后block的数量是
blocksPerGrid = (N - 1) / threadsPerBlock + 1;
比如他是16384的时候gridDim输出出来就是(16384,1,1)
然后。。。。每当block数到32768的时候返回的计算结果就全变成0了，，连gridDim和blockDim都无法输出了。改变threadsPerBlock，比如取512，也是到32768就出错。
随后我把blocksPerGrid改成二维的，x方向512个，y方向根据数组长度定，结果试到512*512都没有再出错，这时gridDim输出出来是(512,512,1)。
问题是，为什么gridDim.x不能到32768？blocksPerGrid定义成了int，dim3的定义也是uint3，不存在溢出问题。

grid中的block数量是有限制的，虽然类型是uint

通过下列代码测试一下你的GPU的性能
————————————————————
#include "../common/book.h"
int main( void ) {
cudaDeviceProp prop;
int count;
HANDLE_ERROR( cudaGetDeviceCount( &count ) );
for (int i=0; i< count; i++) {
HANDLE_ERROR( cudaGetDeviceProperties( &prop, i ) );
printf( " --- General Information for device %d ---\n", i );
printf( "Name: %s\n", prop.name );
printf( "Compute capability: %d.%d\n", prop.major, prop.minor );
printf( "Clock rate: %d\n", prop.clockRate );
printf( "Device copy overlap: " );
if (prop.deviceOverlap)
printf( "Enabled\n" );
else
printf( "Disabled\n");
printf( "Kernel execution timeout : " );
if (prop.kernelExecTimeoutEnabled)
printf( "Enabled\n" );
else
printf( "Disabled\n" );
printf( " --- Memory Information for device %d ---\n", i );
printf( "Total global mem: %ld\n", prop.totalGlobalMem );
printf( "Total constant Mem: %ld\n", prop.totalConstMem );
printf( "Max mem pitch: %ld\n", prop.memPitch );
printf( "Texture Alignment: %ld\n", prop.textureAlignment );
printf( " --- MP Information for device %d ---\n", i );
printf( "Multiprocessor count: %d\n",
prop.multiProcessorCount );
printf( "Shared mem per mp: %ld\n", prop.sharedMemPerBlock );
printf( "Registers per mp: %d\n", prop.regsPerBlock );
printf( "Threads in warp: %d\n", prop.warpSize );
printf( "Max threads per block: %d\n",
prop.maxThreadsPerBlock );
printf( "Max thread dimensions: (%d, %d, %d)\n",
prop.maxThreadsDim[0], prop.maxThreadsDim[1],
prop.maxThreadsDim[2] );
printf( "Max grid dimensions: (%d, %d, %d)\n",
prop.maxGridSize[0], prop.maxGridSize[1],
prop.maxGridSize[2] );
printf( "\n" );
}
}
——————————————————————————————
本人GeForce GTX 850M
Max grid dimensions :(2147483647, 65535, 65535);

我记得cuda高性能运算提到过，block数量写成（x,y,z）形式x的最大值比单写x的大。