HBM Simple

This is a simple example of vector addition to describe how to use HLS kernels with HBM (High Bandwidth Memory) for achieving high throughput.

KEY CONCEPTS: High Bandwidth Memory, Multiple HBM Banks

KEYWORDS: HBM, XCL_MEM_TOPOLOGY, cl_mem_ext_ptr_t

This is Simple example to demonstrate how to use HBM Platform. Two cases are executed, Single HBM bank is used for two inputs and one output; three separate banks are used for each argument of kernels. Individual bank for each buffer will provide more bandwidth for the application.

cl_mem_ext_ptr object needs to be used in cases where memory assignment is done by user.

cl_mem_ext_ptr_t bufExt;
bufExt.obj = source_in1.data();
bufExt.param = 0;
bufExt.flags = n | XCL_MEM_TOPOLOGY; // specify n the bank number which needs to be targeted (0:31)
cl::Buffer buffer_input1(context, CL_MEM_READ_ONLY | CL_MEM_EXT_PTR_XILINX | CL_MEM_USE_HOST_PTR,
                          sizeof(uint32_t) * size, &bufExt, &err));

compute unit interfaces are associated to fixed HBM banks using krnl_vadd.ini file:

[connectivity]
sp=krnl_vadd_1.in1:HBM[0:3]
sp=krnl_vadd_1.in2:HBM[0:3]
sp=krnl_vadd_1.out_r:HBM[0:3]

It specify that kernel interfaces (in1,in2 and out_r) should be connected such a way that it should have access to HBM banks 0 to 3. System linker will make sure this requirement while building the design.

For Case1, all three buffers (in1,in2, and out_r) will be created inside Single bank and application will run and performance will be reported. For Case2, All three buffers will be created into different banks and application will run and performance will be reported. For Case2, three different banks will give higher DDR bandwidth compare to case1, so performance of Case2 will be better compare to case1. Following is the real log reported while running on U280 platform:

Platform Name: Xilinx
Found Device=xilinx_u280_xdma_201920_1
INFO: Reading ./build_dir.hw.xilinx_u280_xdma_201920_1/krnl_vadd.xclbin
Loading: './build_dir.hw.xilinx_u280_xdma_201920_1/krnl_vadd.xclbin'
Running CASE 1  : Single HBM for all three Buffers
Picking Buffer size 67108864 so that all three buffer should fit into Single HBM (max 256MB)
Each buffer is allocated with same HBM bank.
input 1 -> bank 0
input 2 -> bank 0
output  -> bank 0
[CASE 1] THROUGHPUT = 9.54234 GB/s
Running CASE 2: Three Separate Banks for Three Buffers
For This case each buffer will be having different HBM, so buffer size is picked to utilize full HBM
vector size is 268435456 as maximum possible inside single HBM
Each buffer is allocated with different HBM bank.
input 1 -> bank 1
input 2 -> bank 2
output  -> bank 3
[CASE 2] THROUGHPUT = 38.7406 GB/s
TEST PASSED

EXCLUDED PLATFORMS

Platforms containing following strings in their names are not supported for this example :

u200
zc
vck
u250
aws
samsung

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/krnl_vadd.cpp

COMMAND LINE ARGUMENTS

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

./host <krnl_vadd XCLBIN>