Command Queues - 2023.1 English

The clCreateCommandQueue API creates one or more command queues for each device. The FPGA can contain multiple kernels, which can be either the same or different kernels. When developing the host application, there are two main programming approaches to execute kernels on a device:

1. Single out-of-order command queue: Multiple kernel executions can be requested through the same command queue. XRT dispatches kernels as soon as possible, in any order, allowing concurrent kernel execution on the FPGA.
2. Multiple in-order command queue: Each kernel execution is requested from different in-order command queues. In such cases, XRT dispatches kernels from the different command queues, improving performance by running them concurrently on the device.

The following is an example of standard API calls to create in-order and out-of-order command queues.

// Out-of-order Command queue
commands = clCreateCommandQueue(context, device_id, CL_QUEUE_OUT_OF_ORDER_EXEC_MODE_ENABLE, &err);

// In-order Command Queue
commands = clCreateCommandQueue(context, device_id, 0, &err);