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OpenCL: why there is so big difference between the time counter of cl_profiling_info ?

willhua

I run an OpenCL task on Mali G-57 GPU, and profile the performance of kernel by code below:

cl_int err = clEnqueueNDRangeKernel(pocl->getCommandQueue(), kernel, 2, NULL, globalsize, localsize, 0, NULL, &event_kernel );
clWaitForEvents(1, &event_kernel);
cl_ulong queue_time = 0, submit_time = 0, start_time = 0, end_time = 0;
    err = clGetEventProfilingInfo(event_kernel, CL_PROFILING_COMMAND_QUEUED, sizeof(queue_time), &queue_time, 0);
    checkErr(err, "CL_PROFILING_COMMAND_QUEUED", true);
    err = clGetEventProfilingInfo(event_kernel, CL_PROFILING_COMMAND_SUBMIT, sizeof(queue_time), &submit_time, 0);
    checkErr(err, "CL_PROFILING_COMMAND_SUBMIT", true);
    err = clGetEventProfilingInfo(event_kernel, CL_PROFILING_COMMAND_START, sizeof(start_time), &start_time, 0);
    checkErr(err, "CL_PROFILING_COMMAND_START", true);
    err = clGetEventProfilingInfo(event_kernel, CL_PROFILING_COMMAND_END, sizeof(end_time), &end_time, 0);
    checkErr(err, "CL_PROFILING_COMMAND_END", true);
    printf("time value=%llu %llu %llu %llu", queue_time, submit_time, start_time, end_time);
the log shows:
D/OLOG:cl_success:CL_PROFILING_COMMAND_QUEUED
D/OLOG:cl_success:CL_PROFILING_COMMAND_SUBMIT
D/OLOG:cl_success:CL_PROFILING_COMMAND_START
D/OLOG:cl_success:CL_PROFILING_COMMAND_END
D/OLOG:time value=71608492999037 71608493875422 8517593063107986718 8517593063119119891
We can see that the value of CL_PROFILING_COMMAND_START or CL_PROFILING_COMMAND_END is very bigger than CL_PROFILING_COMMAND_QUEUED or CL_PROFILING_COMMAND_SUBMIT. If we chang these to time, the time cost from CL_PROFILING_COMMAND_SUBMIT to CL_PROFILING_COMMAND_START will be 8517521506304ms. It is impossible.
Can anybody tell me what's the wrong which cause the time counter of the task status is so big? 
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