The following figure shows an example with a single out-of-order command queue. The scheduler can dispatch commands from the queue in any order. You must manually define event dependencies and synchronizations as required.
Figure 1. Example with Single Out-of-Order Command Queue
The following is code extracted from host.cpp of the concurrent_kernel_execution_c example that sets up a single out-of-order command queue and enqueues commands as needed:
OCL_CHECK(
err,
cl::CommandQueue ooo_queue(context,
device,
CL_QUEUE_PROFILING_ENABLE |
CL_QUEUE_OUT_OF_ORDER_EXEC_MODE_ENABLE,
&err));
...
printf("[OOO Queue]: Enqueueing scale kernel\n");
OCL_CHECK(
err,
err = ooo_queue.enqueueTask(
kernel_mscale,nullptr, &ooo_events[0]));
set_callback(ooo_events[0], "scale");
...
// This is an out of order queue, events can be executed in any order. Since
// this call depends on the results of the previous call we must pass the
// event object from the previous call to this kernel's event wait list.
printf("[OOO Queue]: Enqueueing addition kernel (Depends on scale)\n");
kernel_wait_events.resize(0);
kernel_wait_events.push_back(ooo_events[0]);
OCL_CHECK(err,
err = ooo_queue.enqueueTask(
kernel_madd,
&kernel_wait_events, // Event from previous call
&ooo_events[1]));
set_callback(ooo_events[1], "addition");
// This call does not depend on previous calls so we are passing nullptr
// into the event wait list. The runtime should schedule this kernel in
// parallel to the previous calls.
printf("[OOO Queue]: Enqueueing matrix multiplication kernel\n");
OCL_CHECK(err,
err = ooo_queue.enqueueTask(
kernel_mmult,
nullptr,
&ooo_events[2]));
set_callback(ooo_events[2], "matrix multiplication");
The Application Timeline view shows that the compute unit mmult_1
is running in parallel with the compute units
mscale_1
and madd_1
, using both multiple in-order queues and single out-of-order queue
methods.
Figure 2. Application Timeline View Showing mult_1 Running with mscale_1
and madd_1