SYCL for OpenCL in a Nutshell

Transcription

1 SYCL for OpenCL in a Nutshell Luke Iwanski, Games Technology Codeplay! SIGGRAPH Vancouver

2 2 Copyright Khronos Group 2014

3 SYCL for OpenCL in a nutshell Copyright Khronos Group 2014 Why? Where in the OpenCL ecosystem? Motivation Features overview Example time Roadmap 3

4 Why SYCL? Modern C++ programming model for OpenCL (compiler, runtime) Ease to use High performance Single source Allows multi-compiler implementation. SYCL device compiler + Host compiler of your choice Portability across platforms and compilers Providing the full OpenCL feature set and seamless integration with existing OpenCL code Enabling the creation of higher level programming models and C++ templated libraries based on OpenCL 4

5 OpenCL ecosystem OpenCL C Kernel Source SPIR Generator (e.g. Khronos patched Clang open source on GitHUB) Alternative Alternative Alternative Language for Language for Language Kernels for Kernels Kernels High-level High-level Apps Frameworks and Frameworks Frameworks SPIR Standard Portable Intermediate Representation SPIR 1.2 Released January 2014! OpenCL Runtime SYCL A programming abstraction that combines the portability and efficiency of OpenCL with the ease of use and flexibility of C++ SYCL 1.2 Provisional Released March 2014 Device X Device Y Device Z 5

6 The layering of SYCL: Building an ecosystem Copyright Khronos Group 2014 User application code C++ template libraries SYCL for OpenCL OpenCL 6

7 Motivation We want to enable C++ for the OpenCL ecosystem Where more C++ developers can get the benefits of OpenCL With C++ libraries supported on OpenCL platforms C++ tools supported on OpenCL platforms Aim to achieve long-term support for OpenCL features with C++ Multiple Sources of implementations (multiple vendors) Reliability by providing host fall-back Enable future innovations 7

8 SYCL features: Overview 8

9 OpenCL/SYCL interoperability Seamless integration of OpenCL C applications with SYCL applications OpenCL C data types and built-in functions available SYCL / OpenGL interoperability Based on OpenCL/OpenGL interoperability extensions C++ exception handling Host fall-back mode - using SYCL without OpenCL Introduced in SYCL Hierarchical data parallelism 9

10 Hierarchical Data Parallelism Workgroup Task (nd-range) Work Work item Workgroup item Work Work item Workgroup item Work Work item Work itemworkgroup Work item Work item Work Work item item Work Work item item item Work item Work Work item Work item Work Work item item item item Work Work item item Work Work item item buffer<int> my_buffer(data, 10); auto in_access = my_buffer.get_access<cl::sycl::access:read>(); auto out_access = my_buffer.access<cl::sycl::access:write>();!command_group(my_queue, [&]() { " parallel_for_workgroup(nd_range(range(size), range(groupsize)), " " lambda<class hierarchical>([=](group group) " { " " parallel_for_workitem(group, [=](item tile) " " { " " " out_access[tile] = in_access[tile] * 2; " " }); " })); }); Advantages:! 1. Easy to understand the concept of work-groups! 2. Performance-portable between CPU and GPU! 3. Barriers are automatically deduced!! 4. Easier to compose components and algorithms 10

11 Example time: Simple kernel 11

12 12 Copyright Khronos Group 2014

13 Simple kernel summary Simple kernel demo source is only 20 lines of actual C++/ SYCL code Equivalent of simple kernel demo in OpenCL takes over 100 lines of code This code can be easily templated by changing 17 lines of code Plain OpenCL C will take many, many,.. many more lines of code 13

14 Example time: Templated kernel 14

15 15 Copyright Khronos Group 2014

16 16 Copyright Khronos Group 2014

17 17 Copyright Khronos Group 2014

18 Templated kernel summary Only 52 lines of code to create a templated kernel for the subtract operation! Templates on the device! factor of 5 lines per new datatype! (including initialisation and printing) SYCL is simple!! 18

19 Final notes about SYCL Keep in mind Advantages of modern C++ (lambdas, templates, struct arguments, static polymorphism) but, limitations of current OpenCL ( recursion, dynamic allocation, static variables) It will get better with the next OpenCL iterations! 19

20 SYCL roadmap GDC, March 2014 Released a provisional specification to enable feedback Developers can provide input into the standardisation process Feedback via Khronos forums Next steps Full specification, based on feedback Khronos test suite for implementations Release of implementations 20

21 SYCL Useful Links SYCL spec and forums: trisycl github: Codeplay s blogs: Examples github 21

22 Thanks! Luke 22