使用二维NDRange workgroup
作为初学者一直，经过多次的上网搜索你一定会看到迈克老狼的向量加法的示例，不知道你是否和我一样，刚开始并不是很准确的知道他的add.cl写的代码的意思，源码如下：
#pragma OPENCL EXTENSION cl_amd_printf : enable
__kernel void vecadd(__global const float* a, __global const float* b, __global float* c) { int x = get_global_id(); int y = get_global_id(); int width = get_global_size(); int height = get_global_size(); if(x == && y ==) printf("%d, %d,%d,%d,%d,%d\n",get_local_size(),get_local_size(),get_local_id(), get_local_id(),get_group_id(),get_group_id()); c[x + y * width] = a[x + y * width] + b[x + y * width]; } 我们在k
这里面我把二维的这些值全部罗列出来如下：
int idx = get_global_id(0);
int idy = get_global_id(1);
uint wiWidth = get_global_size(0);
uint wiHeight = get_global_size(1);
uint gix_t = get_group_id(0);
uint giy_t = get_group_id(1);
uint num_of_blocks_x = get_num_groups(0);
uint num_of_blocks_y = get_num_groups(1);
uint lix = get_local_id(0);
uint liy = get_local_id(1);
你会奇怪为什么他的add.cl优化会这么写：
c[x + y * width] = a[x + y * width] + b[x + y * width];
下面进行分析：
add.cpp关键的代码部分如下（只罗列出部分代码）：
#define width 8//256
#define height 16//256
#define NWITEMS width*height//262144 size_t globalThreads[] = {width, height};
size_t localx, localy; localx = 2;
localy = 4; size_t localThreads[] = {localx, localy}; clEnqueueNDRangeKernel( queue,
kernel,
2,
NULL,
globalThreads,
localThreads, 0, NULL, &ev);
我自己的add.cl代码如下（里面添加啦打印，以便我们可以看出结果）：
int idx = get_global_id();
int idy = get_global_id(); uint wiWidth = get_global_size();
uint wiHeight = get_global_size();
printf("Magnum Global idx = %d, idy = %d, sizeX =%d,sizeY =%d\n",idx,idy,wiWidth,wiHeight); uint gix_t = get_group_id();
uint giy_t = get_group_id();
uint num_of_blocks_x = get_num_groups();
uint num_of_blocks_y = get_num_groups(); printf("Magnum Group idx = %d, idy = %d, blockX=%d,blockY=%d\n",gix_t,gix_t,num_of_blocks_x,num_of_blocks_y); uint lix = get_local_id();
uint liy = get_local_id(); uint LocalX = get_local_size();
uint LocalY = get_local_size(); printf("Magnum Local idx = %d, idy = %d, localX=%d,localY=%d\n\n",lix,liy,LocalX,LocalY);
输出的结果如下：
Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
Magnum Group idx = , idy = , blockX=,blockY=
Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY= Magnum Global idx = , idy = , sizeX =,sizeY =
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Magnum Local idx = , idy = , localX=,localY=
从从这个结果首先能说明几个问题：
首先我们在：
- clEnqueueNDRangeKernel( queue, kernel, , NULL, globalThreads, localThreads, 0, NULL, &ev); 设置维度是2，否则add.cl中所有类似get_local_size(1)将只会返回一。
- 设置GlobaThreads 和 LocalThreads 不一定是 GlobalThreads= {8, 8}; 也可以不相等，LocalThreads也是一样。
- 理解opencl中的内存分布可以理解为二维数组，而且内存寻址的方向就像是：左上角（0，0）为原点，一行一行的扫描下去。
- WorkGroup的大小，目前我认为X，Y可以分开来理解（后面若发现错误我会及时改正） WorkGroup number(x) = GlobalThread(x)/LocalThread(x).
- 最小的单位是LocalX * LocalY, 然后用总的GlobalThreads按照这个单位进行分割成一个一个的组。每个二维的小单位还是一行一行的扫描过去的。目前我们的这个是8*16，你会发现总的Thread也是8*16，对应的每一个线程执行一次加法操作，有人会问可不可以不用这么多呢,用4*16个Threads,每个线程里面做两次加法动作，其实是可以的，这个原则是根据你的具体的Device来说的，当前我们说的是Device是GPU，比如你的GPU当前支持最大的线程数是1024*1024，这种情况，你不用多的，而是用少的线程来做，会降低你的效率，你需要尽可能的让Device满负荷工作这样才能达到提高运算速度。
继续分析为什么 NDRange改成二维的之后,add.cl变成：
c[x + y * width] = a[x + y * width] + b[x + y * width]; 因为在CPU端每个 C[8*16],通过打印可以在这里C[x+y*width]，x 最大是7，width是8,y最大是17，只有这样才能做完所有的向量相加。
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