CL_DEVICE_MAX_WORK_ITEM_SIZES ：线程分组的尺寸限制

　　CL_DEVICE_MAX_WORK_GROUP_SIZE：线程分组中所能包含的最大线程数

　　Thread blocks have maximum dimensions： CL_DEVICE_MAX_WORK_ITEM_SIZES，Think of laying out your threads in a grid， you can't have a row with more than 512 threads. You can't have a column with more than 512 threads. And you can't stack more than 64 threads high. Next， there is a maximum： CL_DEVICE_MAX_WORK_GROUP_SIZE number of threads， 512， that can be grouped together in a block. So your thread blocks dimensions could be：