SYCL (Khronos SYCL) is an open standard for single-source heterogeneous programming that uses C++ templates. It aims to provide a more native C++ interface for OpenCL-like programming while retaining compatibility with OpenCL. The key aspects covered are the SYCL programming model which supports most C++11/14 features, its single-source approach across devices, and memory model including shared virtual memory. However, it currently lacks official implementations and support is mainly through the triSYCL library.

1. C++ Single-Source Heterogeneous Programming for OpenCL
Khronos SYCL
Bekket McClane
@ Advanced Programming
Language, Jenq-Kuen Lee
2016 Spring, NTHU

2. Syllabus
❖ Heterogeneous Computing By OpenCL
❖ Introducing to SYCL
❖ SYCL Internals
❖ Programming Model
❖ Execution Model
❖ Memory Model
❖ Summary

3. OpenCL
Host Program
(C/C++, …)
OpenCL Kernel
(OpenCL C)
Dispatch
Propertied
Device Compiler
Accelerated
Devices
(GPU, DSP…)
SPIR-V
Compiler
Source
Propertied
SPIR-V Compiler
SPIR-V

4. OpenCL the Bad Part 1

5. OpenCL the Bad Part 1
Kernel Code

6. OpenCL the Bad Part 1
Kernel Code
Host Code

7. OpenCL the Bad Part 2

8. OpenCL the Bad Part 3
OPENCL
(CPU) FALLBACK IMPLEMENTATION?

9. OpenCL the Bad Part 3
OPENCL
(CPU) FALLBACK IMPLEMENTATION?

10. SYCL Start Up

11. SYCL Start Up
Single Source

12. SYCL Start Up
Single Source
Multiple Implementations

13. SYCL Programming Model
❖ All C++14 features. Except Runtime Type Information(RTTI)
❖ Exception Handling
❖ C++11 lambda
❖ C++11 variadic templates, template aliases
❖ C++11 rvalue reference
❖ C++11 std::function, std::string, std::vector

14. SYCL Data Parallel 101

15. SYCL Data Parallel With Workgroup

16. SYCL Execution Model
❖ Platforms
❖ Devices
❖ Command Queue
❖ Command Group
❖ Kernel
❖ Context
❖ Program
Terms

17. SYCL Execution Model
❖ Platforms
❖ Devices
❖ Command Queue
❖ Command Group
❖ Kernel
❖ Context
❖ Program
Terms
Same as OpenCL

18. SYCL Command Group
❖ Group of OpenCL commands
❖ Commands in group are executed in-order
❖ The smallest scheduling unit
❖ Different command groups may executed out-of-order

19. SYCL Command Group

20. SYCL Kernel

21. SYCL Kernel

22. SYCL Device-side Enqueue
❖ Has same behavior as that in OpenCL 2.x
❖ Sub-kernel has separated command queue
❖ Use out-of-order command queue like OpenCL
(No command group?)
❖ Use events to manage command orders
❖ No concrete examples so far

23. SYCL Memory Model
❖ Global, Constant, Local, Private just like OpenCL
❖ cl::sycl::accessor
❖ cl::sycl::buffer : Unified handle to many kinds of
memory
❖ Allow Shared Virtual Memory
❖ Allow atomic access

24. SYCL Local Variables

25. SYCL Local Variables

26. Powerful Accessor Template
• Read
• Write
• Read/Write Atomic Related*
SVM Related

27. SYCL Shared Virtual Memory

28. SYCL Shared Virtual Memory
SVM buffer allocation

29. SYCL Shared Virtual Memory
Host Access
SVM buffer allocation

30. SYCL Shared Virtual Memory
Host Access
SVM buffer allocation
Device Access

31. SYCL the Good Part - Memory
❖ Both cl::sycl::buffer and cl::sycl::accessor
encapsulate underlying memory into a “handle”
❖ The “handle” provides a flexible way to manipulate data
❖ Adoption of C++ template reserves spaces for features in
the future

32. Summary

33. triSYCL
❖ Use Boost library(http://www.boost.org) to simulate
❖ The only implementation(and header files) seen so far
❖ Latest SYCL 2.2!
❖ Need to be compiled with C++14 ! (-std=c++14)
https://github.com/amd/triSYCL

34. SYCL the Missing Part
❖ Where are the (official)header files?
❖ Little examples
❖ SYCL to SPIR-V compiler?
❖ Still a young project

35. SYCL in a Nutshell
❖ Single source. Neat syntax
❖ All the shiny C++ features
❖ Easy-implement fallbacks
❖ Follow the version(steps) of OpenCL
❖ No real devices(platforms) available for playing so far
❖ *NOT intended to replace OpenCL
(Still needs exist OpenCL drivers/implementations)

36. Thank You
Q & A