2018-04-11 获取命令队列信息大小

NDRange & single workitem

http://downloads.ti.com/mctools/esd/docs/opencl/execution/kernels-workgroups-workitems.html
如果内核使用单个工作项来执行——比如运行在一个CPU上，那么可以用下列函数：
clEnqueueTask (cl_command_queue command_queue, cl_kernel kernel, cl_uint num_events_in_wait_list, const cl_event *event_wait_list, cl_event *event)

OpenCL入门介绍
https://blog.csdn.net/u012361418/article/details/46475885

内核执行
一个执行内核的命令，必须排队到命令队列
clEnqueueNDRangeKernel()
    数据并行执行模型
    描述内核执行的索引空间
    需要NDRandge()维度和工作组大小的信息
clEnqueueTask()
    任务并行执行模型(多队列任务)
    内核在单工作项上执行
clEnqueueNativeKernel()
    任务并行执行模型
    执行一个未编译的本地C/C++函数，使用OpenCL编译器
    此模式不使用内核对象，因此参数必须被传递

---

OpenCL异构并行计算编程笔记(2)：命令队列与内存对象

http://blog.csdn.net/catalyst_zx/article/details/52818557

cl_int ret;               //用于保存函数返回值  
cl_context_properties context_props[] = { CL_CONTEXT_PLATFORM, (cl_context_properties)platform[1], 0 };     //用于设置命令队列属性  
size_t ext_size;          //用于保存命令队列信息大小  
char *ext_data;          //用于保存命令队列信息  
cl_platform_info command_queue_info = CL_QUEUE_COMTEXT;    //设置所要查询的信息  
  
//建立命令队列  
cl_context command_queue = clCreateContext(context, device, context_props, &ret);  
//获取命令队列信息大小  
ret = clGetCommandQueueInfo(command_queue, command_queue_info, context_props, NULL, ext_size)  

//为ext_data分配空间大小  
ext_data = new char[ext_size];  
//获取命令队列信息  
ret = clGetCommandQueueInfo(command_queue, command_queue_info, ext_size, ext_data, NULL);  
  
std::cout << ext_data << std::endl;     //输出命令队列信息 

---

get_global_size

https://www.cnblogs.com/biglucky/p/3755189.html
uint get_work_dim() : 返回线程调度的维度数。
uint get_global_size(uint dimension) : 返回在所请求维度上work_item的总数。
uint get_global_id(uint dimension) : 返回在所请求的维度上当前work_item在全局空间中的索引。
uint get_local_size(uint dimension) : 返回在所请求的维度上work-group的大小。
uint get_local_id(uint dimension) : 返回在所请求的维度上，当前work_item在work_group中的索引。
uint get_number_groups(uint dimension) : 返回在所请求维度上work-group的数目，这个值等于get_global_size 除以 get_local_size。
uint get_group_id(uint dimension) : 返回在所请求的维度上当前wrok_group在全局空间中的索引。

---

Re: basic question regarding get_global_id
get_global_id returns the number for the current thread. The parameter is just the dimension of the array of threads. When you enqueue a kernel, one of the parameters is an int array global_work_size. If global_work_size is an int[2] (2 dimensional array of threads) then each thread will have a 2 dimensional identifier. Lets say global_work_size[0] = 3 and global_work_size[1] = 3 then there will be 3 * 3 = 9 threads in total in a grid something like this:

-----------------
| 0,0 | 0,1 | 0,2 |
-----------------
| 1,0 | 1,1 | 1,2 |
-----------------
| 2,0 | 2,1 | 2,2 |
-----------------

So the thread in the top left corner will have get_global_id(0) = 0 and get_global_id(1) = 0; The one just below it will have get_global_id(0) = 1 and get_global_id(1) = 0.
Edit: have a look at this link for another picture that might help: http://www.khronos.org/message_board...hp?f=28&t=5375.

-----------------
| global_id(0,0) | global_id(0,1) | global_id(0,2) |
-----------------
| global_id(1,0) | global_id(1,1) | global_id(1,2) |
-----------------
| global_id(2,0) | global_id(2,1) | global_id(2,2) |
-----------------

For Thread(1,2):
get_global_id = (1,2) ???
get_global_id(0) = 1
get_global_id(1) = 2