OpenCL 1.0 Specification阅读笔记（7）

Executing Kernels

 

// enqueue a command to execute a kernel on a devicecl_int clEnqueueNDRangeKernel( cl_command_queue command_queue, cl_kernel kernel, cl_uint work_dim, const size_t *global_work_offset, const size_t *global_work_size, const size_t *local_work_size, cl_uint num_events_in_wait_list, const cl_event *event_wait_list, cl_event *event);

global_work_offset现在为NULL

global_work_size为总线程数

local_work_size为一个group的线程数，group中的线程必须在一个处理器中运行，不同group的线程可能在不同的处理器上，同步代价很大，local_work_size可以为NULL，driver为其设定划分，不推荐。

 

// enqueues a command to execute a kernel on a device. The kernel is executed using a single work-itemcl_int 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 );// enqueues a command to execute a native c/c++ funtion not compiled using the OpenCL compilercl_int clEnqueueNativeKernel( cl_command_queue command_queue, void (*user_func)(void *), void *args, size_t cb_args, cl_uint num_mem_objects, const cl_mem *mem_list, const void **args_mem_loc, cl_uint num_events_in_wait_list, const cl_event *event_wait_list, cl_event *event);

 

 

Event Objects

 

Event objects can be used to refer to a kernel execution command or read, write, map and copy commands on memory objects

 

event object可以用来跟踪命令执行的状态，每当向command queue中加入command，都会返回一个event object（如果成功的话），这些状态包括：

（1）CL_QUEUED：命令入队

（2）CL_SUBMITTED：入队的命令已经提交给设备

（3）CL_RUNNING：命令正在设备上执行

（4）CL_COMPLETE：命令已经完成或者返回错误标识（负数）

 

clWaitForEvents(): waits on the host thread for commands identified by event objects in event_list to complete

clGetEventInfo(): returns information about the event object

clRetainEvent(): increments the event reference count

clReleaseEvent(): decrements the event reference count

 

Out of order Execution

 

clEnqueueMarker(): enqueue a marker command to command_queue. The marker command returns an event which can be used by to queue a wait on this event, i.e. wait for all commands queued before the marker command to complete.插了一个fence呗

 

clEnqueueWaitForEvents(): enqueue a wait for  a specific  event or a list of events to complete before any further commands queued in the command-queue are executed.插了一个Wait。

 

clEnqueueBarrier():直接插一个同步点

 

Profiling Operations on Memory Objects and Kernels

 

需要创建command queue时指定Profiling Enable

 

clGetEventProfilingInfo()：return profiling information for the command associated with event

仅有命令入队、提交、开始和结束的时间，nanoseconds

 

Flush and Finish

 

// issues all previously queued OpenCL commands in command_queue to the device associated with command_queuecl_int clFlush( cl_command_queue command_queue);// blocks until all preivous queued OpenCL commands in command_queue are issued to the assoicated device and have completecl_int clFinish( cl_command_queue command_queue);