Getting Started With OpenCL: Using The ODROID-XU4

While I tested OpenGL ES with tools like glmark2-es2 and es2gears, as well as WebGL demos in Chromium, I did not test OpenCL, since I’m not that familiar with it, except it’s used for GPGPU (General Purpose GPU) to accelerate tasks like image/audio processing. That was a good excuse to learn a bit more, try it out on the board, and write a short guide to get started with OpenGL on hardware with Arm Mali GPU. The purpose of this tutorial is to show how to run an OpenCL sample, and OpenCL utility, and I won’t go into the nitty gritty of OpenCL code. If you want to learn more about OpenCL coding on Arm, one way would be to check out the source code of the provided samples. Arm Compute Library and OpenCL Samples Since I did not know where to start, Hardkernel redirected me to a forum thread where we are shown how to use Arm Compute Library to test OpenCL on the board. The relevant post is dated January 2018, and relies on Compute Library 17.12, but you can check out the latest version and documentation here, https://arm-software.github.io/ComputeLibrary/latest/. The latest version is 18.03 at the time of writing this post, so I retrieved it, and tried to build it as instructed:

$ wget https://github.com/ARM-software/ComputeLibrary/archive/v18.03.tar.gz
$ tar xvf v18.03.tar.gz
$ cd ComputeLibrary-18.03/
$ sudo apt install scons
$ scons Werror=1 -j8 debug=0 neon=1 opencl=1 embed_kernels=1 os=linux arch=armv7a build=native

However, It failed with:

$ g++: internal compiler error: Killed (program cc1plus)

Looking at the kernel log with dmesg, it was clear the board ran out of memory: “Out of memory: Kill process 4984 (cc1plus) Out of memory: Kill process 4984 (cc1plus)“. So I had to setup a swap file (1GB):

$ sudo dd if=/dev/zero of=/swapfile bs=1024 count=1M
$ sudo chown root.root /swapfile
$ sudo chmod 0600 /swapfile
$ sudo mkswap /swapfile
$ sudo swapon /swapfile

The swap file gave us more memory:

free -m
total used free shared buff/cache available
Mem: 1994 336 520 34 1137 1568
Swap: 1023 0 1023

I restarted the build with NEON and OpenCL enabled:

$ scons Werror=1 -j8 debug=0 neon=1 opencl=1 embed_kernels=1 os=linux arch=armv7a build=native

This time it completed:

scons: done building targets.

Update

Setting up ZRAM instead of swap is usually better in case you run out of memory, as described at https://www.cnx-software.com/2018/05/14/running-out-of-ram-in-ubuntu-enable-zram/. We can copy the libraries to /usr/lib, which gives us a bunch of samples to play with:

$ sudo cp build/*.so /usr/lib/
$ ls examples/
SConscript graph_mobilenet_qasymm8.cpp
cl_convolution.cpp graph_resnet50.cpp
cl_events.cpp graph_squeezenet.cpp
cl_sgemm.cpp graph_squeezenet_v1_1.cpp
gc_absdiff.cpp graph_vgg16.cpp
gc_dc.cpp graph_vgg19.cpp
graph_alexnet.cpp neon_cartoon_effect.cpp
graph_googlenet.cpp neon_cnn.cpp
graph_inception_v3.cpp neon_convolution.cpp
graph_inception_v4.cpp neon_copy_objects.cpp
graph_lenet.cpp neon_scale.cpp
graph_mobilenet.cpp neoncl_scale_median_gaussian.cpp

Note that some are NEON only, not using OpenCL, and the prefix explains the type of sample:

cl_*.cpp –> OpenCL examples
gc_*.cpp –> GLES compute shaders examples
graph_*.cpp –> Graph examples
neoncl_*.cpp –> NEON / OpenCL interoperability examples
neon_*.cpp –> NEON examples

All samples have also been built and can be found in the build/examples directory. I ran cl_convolution after generating a Raw ppm image using Gimp:

$ time ./cl_convolution ~/ODROID-XU4Q-Large.ppm
$ ./cl_convolution

Test passed

real 0m5.814s
user 0m4.893s
sys 0m0.758s

It processed the photo (5184 x 3456) in less than 6 seconds. If we look at the resulting image, we can see the grayscale output from the OpenCL convolution, as shown in Figure 1.

Figure 01 - Original Image (Left) vs After OpenCL Convolution (Right)

I’ve repeated a similar operation with convert which has not been compiled with OpenCL support, using software only:

$ time convert ODROID-XU4Q-Large.ppm -colorspace Gray ODROID-XU4Q-Large-Grayscale.ppm

real 0m10.475s
user 0m0.724s
sys 0m2.957s

It took a little over 10 seconds, so almost twice the time used by the OpenCL demo. The PPM image files are however over 50MB, so part of the time is used to read and save the file from the eMMC flash. Repeating the tests provide similar performance (~6s vs ~11s), so it may be negligible. The “convert version” command’s output showing OpenCL is not part of the enabled features in ImageMagick:

$ convert -version
Version: ImageMagick 6.9.7-4 Q16 arm 20170114 http://www.imagemagick.org
Copyright: © 1999-2017 ImageMagick Studio LLC
License: http://www.imagemagick.org/script/license.php
Features: Cipher DPC Modules OpenMP
Delegates (built-in): bzlib djvu fftw fontconfig freetype jbig jng jpeg lcms lqr ltdl lzma openexr pangocairo png tiff wmf x xml zlib

It’s fun, so I tried another sample:

$ time ./cl_events ~/ODROID-XU4Q-Large.ppm
$ ./cl_events

Test passed

real 0m3.068s
user 0m2.527s
sys 0m0.369s

What did it do? When I open the file it looks the same of the first sample (Grayscale image), but it actually scaled the image (50% width, 50% height):

$ file ~/ODROID-XU4Q-Large.ppm_out.ppm
/home/odroid/ODROID-XU4Q-Large.ppm_out.ppm: Netpbm image data, size = 2592 x 1728, rawbits, pixmap

The last sample cl_sgemm manipulates matrices. The main goal of the three OpenCL (cl_xxx_ samples) is to show how to use OpenCL Convolution, Events and SGEMM (Single-precision GEneral Matrix Multiply) using the Compute Library. You can also play with other samples for NEON and OpenGL ES, and ARM Community published a blog post explaining how to run neon_cartoon_effect on Raspberry Pi , and explaining the source code in details. You don’t actually need an RPi board for that since any ARM board with a processor supporting NEON should work.

clinfo Utility

clinfo is a utility that print information about OpenCL platforms and devices in the system, https://github.com/Oblomov/clinfo, which is easily installed:

$ sudo apt install clinfo

However, running the program does not return any useful information:

$ clinfo
Number of platforms 0

This is not what I expected. Luckily, setting up clinfo is explained in the ODROID Magazine article at https://magazine.odroid.com/article/clinfo-compiling-the-essential-opencl-gpu-tuning-utility-for-the-odroid-xu4/, so let’s have a try. We need to use Mali’s framebuffer driver, then setup the vendor ICD file:

$ sudo apt install mali-fbdev
$ sudo mkdir -p /etc/OpenCL/vendors
$ sudo sh -c 'echo "/usr/lib/arm-linux-gnueabihf/mali-egl/libOpenCL.so" > /etc/OpenCL/vendors/armocl.icd'

Now we can run clinfo:

$ clinfo
Number of platforms 1
Platform Name ARM Platform
Platform Vendor ARM
Platform Version OpenCL 1.2 v1.r12p0-04rel0.03af15950392f3702b248717f4938b82
Platform Profile FULL_PROFILE
Platform Extensions cl_khr_global_int32_base_atomics cl_khr_global_int32_extended_atomics cl_khr_local_int32_base_atomics cl_khr_local_int32_extended_atomics cl_khr_byte_addressable_store cl_khr_3d_image_writes cl_khr_fp64 cl_khr_int64_base_atomics cl_khr_int64_extended_atomics cl_khr_fp16 cl_khr_gl_sharing cl_khr_icd cl_khr_egl_event cl_khr_egl_image cl_arm_core_id cl_arm_printf cl_arm_thread_limit_hint cl_arm_non_uniform_work_group_size cl_arm_import_memory
Platform Extensions function suffix ARM

Platform Name ARM Platform
Number of devices 2
Device Name Mali-T628
Device Vendor ARM
Device Vendor ID 0x6200010
Device Version OpenCL 1.2 v1.r12p0-04rel0.03af15950392f3702b248717f4938b82
Driver Version 1.2
Device OpenCL C Version OpenCL C 1.2 v1.r12p0-04rel0.03af15950392f3702b248717f4938b82
Device Type GPU
Device Profile FULL_PROFILE
Device Available Yes
Compiler Available Yes
Linker Available Yes
Max compute units 4
Max clock frequency 600MHz
Device Partition (core)
Max number of sub-devices 0
Supported partition types None
Max work item dimensions 3
Max work item sizes 256x256x256
Max work group size 256
Preferred work group size multiple 4
Preferred / native vector sizes
char 16 / 16
short 8 / 8
int 4 / 4
long 2 / 2
half 8 / 8 (cl_khr_fp16)
float 4 / 4
double 2 / 2 (cl_khr_fp64)
Half-precision Floating-point support (cl_khr_fp16)
Denormals Yes
Infinity and NANs Yes
Round to nearest Yes
Round to zero Yes
Round to infinity Yes
IEEE754-2008 fused multiply-add Yes
Support is emulated in software No
Single-precision Floating-point support (core)
Denormals Yes
Infinity and NANs Yes
Round to nearest Yes
Round to zero Yes
Round to infinity Yes
IEEE754-2008 fused multiply-add Yes
Support is emulated in software No
Correctly-rounded divide and sqrt operations No
Double-precision Floating-point support (cl_khr_fp64)
Denormals Yes
Infinity and NANs Yes
Round to nearest Yes
Round to zero Yes
Round to infinity Yes
IEEE754-2008 fused multiply-add Yes
Support is emulated in software No
Address bits 64, Little-Endian
Global memory size 2090397696 (1.947GiB)
Error Correction support No
Max memory allocation 522599424 (498.4MiB)
Unified memory for Host and Device Yes
Minimum alignment for any data type 128 bytes
Alignment of base address 1024 bits (128 bytes)
Global Memory cache type Read/Write
Global Memory cache size 131072 (128KiB)
Global Memory cache line size 64 bytes
Image support Yes
Max number of samplers per kernel 16
Max size for 1D images from buffer 65536 pixels
Max 1D or 2D image array size 2048 images
Max 2D image size 65536x65536 pixels
Max 3D image size 65536x65536x65536 pixels
Max number of read image args 128
Max number of write image args 8
Local memory type Global
Local memory size 32768 (32KiB)
Max number of constant args 8
Max constant buffer size 65536 (64KiB)
Max size of kernel argument 1024
Queue properties
Out-of-order execution Yes
Profiling Yes
Prefer user sync for interop No
Profiling timer resolution 1000ns
Execution capabilities
Run OpenCL kernels Yes
Run native kernels No
printf() buffer size 1048576 (1024KiB)
Built-in kernels
Device Extensions cl_khr_global_int32_base_atomics cl_khr_global_int32_extended_atomics cl_khr_local_int32_base_atomics cl_khr_local_int32_extended_atomics cl_khr_byte_addressable_store cl_khr_3d_image_writes cl_khr_fp64 cl_khr_int64_base_atomics cl_khr_int64_extended_atomics cl_khr_fp16 cl_khr_gl_sharing cl_khr_icd cl_khr_egl_event cl_khr_egl_image cl_arm_core_id cl_arm_printf cl_arm_thread_limit_hint cl_arm_non_uniform_work_group_size cl_arm_import_memory

Device Name Mali-T628
Device Vendor ARM
Device Vendor ID 0x6200010
Device Version OpenCL 1.2 v1.r12p0-04rel0.03af15950392f3702b248717f4938b82
Driver Version 1.2
Device OpenCL C Version OpenCL C 1.2 v1.r12p0-04rel0.03af15950392f3702b248717f4938b82
Device Type GPU
Device Profile FULL_PROFILE
Device Available Yes
Compiler Available Yes
Linker Available Yes
Max compute units 2
Max clock frequency 600MHz
Device Partition (core)
Max number of sub-devices 0
Supported partition types None
Max work item dimensions 3
Max work item sizes 256x256x256
Max work group size 256
Preferred work group size multiple 4
Preferred / native vector sizes
char 16 / 16
short 8 / 8
int 4 / 4
long 2 / 2
half 8 / 8 (cl_khr_fp16)
float 4 / 4
double 2 / 2 (cl_khr_fp64)
Half-precision Floating-point support (cl_khr_fp16)
Denormals Yes
Infinity and NANs Yes
Round to nearest Yes
Round to zero Yes
Round to infinity Yes
IEEE754-2008 fused multiply-add Yes
Support is emulated in software No
Single-precision Floating-point support (core)
Denormals Yes
Infinity and NANs Yes
Round to nearest Yes
Round to zero Yes
Round to infinity Yes
IEEE754-2008 fused multiply-add Yes
Support is emulated in software No
Correctly-rounded divide and sqrt operations No
Double-precision Floating-point support (cl_khr_fp64)
Denormals Yes
Infinity and NANs Yes
Round to nearest Yes
Round to zero Yes
Round to infinity Yes
IEEE754-2008 fused multiply-add Yes
Support is emulated in software No
Address bits 64, Little-Endian
Global memory size 2090397696 (1.947GiB)
Error Correction support No
Max memory allocation 522599424 (498.4MiB)
Unified memory for Host and Device Yes
Minimum alignment for any data type 128 bytes
Alignment of base address 1024 bits (128 bytes)
Global Memory cache type Read/Write
Global Memory cache size 131072 (128KiB)
Global Memory cache line size 64 bytes
Image support Yes
Max number of samplers per kernel 16
Max size for 1D images from buffer 65536 pixels
Max 1D or 2D image array size 2048 images
Max 2D image size 65536x65536 pixels
Max 3D image size 65536x65536x65536 pixels
Max number of read image args 128
Max number of write image args 8
Local memory type Global
Local memory size 32768 (32KiB)
Max number of constant args 8
Max constant buffer size 65536 (64KiB)
Max size of kernel argument 1024
Queue properties
Out-of-order execution Yes
Profiling Yes
Prefer user sync for interop No
Profiling timer resolution 1000ns
Execution capabilities
Run OpenCL kernels Yes
Run native kernels No
printf() buffer size 1048576 (1024KiB)
Built-in kernels
Device Extensions cl_khr_global_int32_base_atomics cl_khr_global_int32_extended_atomics cl_khr_local_int32_base_atomics cl_khr_local_int32_extended_atomics cl_khr_byte_addressable_store cl_khr_3d_image_writes cl_khr_fp64 cl_khr_int64_base_atomics cl_khr_int64_extended_atomics cl_khr_fp16 cl_khr_gl_sharing cl_khr_icd cl_khr_egl_event cl_khr_egl_image cl_arm_core_id cl_arm_printf cl_arm_thread_limit_hint cl_arm_non_uniform_work_group_size cl_arm_import_memory

NULL platform behavior
clGetPlatformInfo(NULL, CL_PLATFORM_NAME, ...) ARM Platform
clGetDeviceIDs(NULL, CL_DEVICE_TYPE_ALL, ...) Success [ARM]
clCreateContext(NULL, ...) [default] Success [ARM]
clCreateContextFromType(NULL, CL_DEVICE_TYPE_DEFAULT) Success (1)
Platform Name ARM Platform
Device Name Mali-T628
clCreateContextFromType(NULL, CL_DEVICE_TYPE_CPU) No devices found in platform
clCreateContextFromType(NULL, CL_DEVICE_TYPE_GPU) Success (2)
Platform Name ARM Platform
Device Name Mali-T628
Device Name Mali-T628
clCreateContextFromType(NULL, CL_DEVICE_TYPE_ACCELERATOR) No devices found in platform
clCreateContextFromType(NULL, CL_DEVICE_TYPE_CUSTOM) No devices found in platform
clCreateContextFromType(NULL, CL_DEVICE_TYPE_ALL) Success (2)
Platform Name ARM Platform
Device Name Mali-T628
Device Name Mali-T628

ICD loader properties
ICD loader Name OpenCL ICD Loader
ICD loader Vendor OCL Icd free software
ICD loader Version 2.2.11
ICD loader Profile OpenCL 2.1

That’s a lot of information, and it shows one platform with two OpenCL devices (both Mali-T628) supporting OpenCL 1.2.

That’s all for this little getting started guide. If you actually want to make something with OpenCL, it’s time to read Arm Compute Library documentation, and other resources on the web.