Loop Pipelining¶

This example demonstrates how loop pipelining can be used to improve the performance of a kernel.

KEY CONCEPTS: Kernel Optimization, Loop Pipelining

This example demonstrates how loop pipelining can be used to improve the performance of a kernel. Pipelining is a technique to increase instruction level parallelism in the hardware implementation of an algorithm by overlapping independent stages of operations and functions.

Two kernels kernel_vadd and kernel_pipelined are used for comparison in performance. Kernel execution time will be less for the pipelined kernel as it uses pragma HLS PIPELINE in read and write loops which enables burst transfers resulting in effective usage of bandwidth of m_axi in interface.

read_a:
        for (int x = 0; x < N; ++x) {
           #pragma HLS LOOP_TRIPCOUNT min=c_n max=c_n
           #pragma HLS PIPELINE II=1
            result[x] = a[i * N + x];
        }

Following is the log reported while running the design on U250 platform:

Platform Name: Xilinx
INFO: Reading build_dir.hw.xilinx_u250_gen3x16_xdma_3_1_202020_1/vector_addition.xclbin
Loading: 'build_dir.hw.xilinx_u250_gen3x16_xdma_3_1_202020_1/vector_addition.xclbin'
Trying to program device[0]: xilinx_u250_gen3x16_xdma_shell_3_1
Device[0]: program successful!
|-------------------------+-------------------------|
| Kernel                  |    Wall-Clock Time (ns) |
|-------------------------+-------------------------|
| vadd: simple            |                   66858 |
| vadd: pipelined         |                   16410 |
|-------------------------+-------------------------|
| Speedup                 |                4.074223 |
|-------------------------+-------------------------|
Note: Wall Clock Time is meaningful for real hardware execution only, not for emulation.
Please refer to profile summary for kernel execution time for hardware emulation.
TEST PASSED.

EXCLUDED PLATFORMS:

All NoDMA Platforms, i.e u50 nodma etc

DESIGN FILES¶

Application code is located in the src directory. Accelerator binary files will be compiled to the xclbin directory. The xclbin directory is required by the Makefile and its contents will be filled during compilation. A listing of all the files in this example is shown below

src/host.cpp
src/vector_addition.cpp
src/vector_addition_BAD.cpp

Access these files in the github repo by clicking here.

COMMAND LINE ARGUMENTS¶

Once the environment has been configured, the application can be executed by

./loop_pipeline <vector_addition XCLBIN>