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Thread: How can I wait for on-device queue?

  1. #1
    Junior Member
    Join Date
    Sep 2012
    Posts
    20

    How can I wait for on-device queue?

    I'm learning OpenCL 2.0 and stuck at synchronization of child kernels and parent kernels in a simple dynamic parallelism algorithm.

    When its just incrementing a single value, it seems to be working but when I add more real world code, child kernels do not finish before the parent kernel finishes.

    I tried clFinish() for on-device queue, it returned invalid queue error.

    Then tried clenqueuemarkerwithwaitlist(to connect the host queue with device queue so both finish before reading result buffers) which returned same error again.

    Then realized documentation says there are for host queues.

    How can I wait for an on-device queue?


    My intention is to finish all device side queues before buffer read commands start. It doesn't matter if child kernel starts after parent kernel or at the same time. I just want to make child-kernel data-array adjustments visible on host queue so when I call clFinish on that host queue, memory will be consistent.



    A working(or fooling me as if its working) example:

    Code :
                    __kernel void testDynamic(__global int *data)
                    {
                        int id=get_global_id(0);
                        atomic_add(&data[1],2);
                    }
     
                    __kernel void test(__global int * data)
                    {
                        int id=get_global_id(0);
                        atomic_add(&data[0],2);
                        if (id == 0) {
                            queue_t q = get_default_queue();
                            ndrange_t ndrange = ndrange_1D(1,1);
                            void (^my_block_A)(void) = ^{
                                testDynamic(data);};
                            enqueue_kernel(q, CLK_ENQUEUE_FLAGS_WAIT_KERNEL,
                                           ndrange,
                                           my_block_A);
                        }
     
                    }

    a non-working example:

    Code :
                            __kernel void test( __global float *xyz,__global float *xyzn,__global float *xyzo,__global float * arguments)
                            {
                                int threadId=get_global_id(0);
                                float dx=xyz[threadId*3]-arguments[2];float dy=xyz[threadId*3+1]-arguments[3];float t=arguments[1];
                                float ctr=arguments[0];float wave=0.02f*ctr*sin(40.0f*t+100.0f*sqrt(dx*dx+dy*dy));
                                xyzo[threadId*3]=xyz[threadId*3]+xyzn[threadId*3]*wave; // wave equation for all surface vertices
                                xyzo[threadId*3+1]=xyz[threadId*3+1]+xyzn[threadId*3+1]*wave; // wave equation for all surface vertices
                                xyzo[threadId*3+2]=xyz[threadId*3+2]+xyzn[threadId*3+2]*wave; // wave equation for all surface vertices
                            }
     
                            __kernel void waveEquation( __global float *xyz,__global float *xyzn,__global float *xyzo,__global float * arguments)
                            {
                                int threadId=get_global_id(0);
                                if(threadId<arguments[4])
                                {
                                        queue_t q = get_default_queue();
                                        ndrange_t ndrange = ndrange_1D(threadId,1,1);
                                        void (^my_block_A)(void) = ^{test(xyz,xyzn,xyzo,arguments);};
                                        enqueue_kernel(q, CLK_ENQUEUE_FLAGS_NO_WAIT,ndrange,my_block_A);
     
                                }
     
                            }

    above code not only malfunctioning but also randomly malfunctioning for the first 1000-2000 workitems (some of them can actually update their data before host synchronizes on data).
    Last edited by Tugrul; 07-02-2017 at 05:55 AM.

  2. #2
    Junior Member
    Join Date
    Sep 2012
    Posts
    20
    Also it could be a queue-size issue on rx550's implementation. Enqueueing nearly 64k child kernels may not be a good design maybe? How can I make a ray-tracer then? Each ray will refract+reflected for an unknown times using same function and each ray will be computed by 1 workitem. returned value of enqueue_kernel is SUCCESS. Even tried compile options in clBuildProgram and checked against detailed errors such as queue-full and similar.

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