opencl sycl bof - siggraph 2014
DESCRIPTION
SYCL slide presentation from the 2014 SIGGRAPH BOFTRANSCRIPT
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SYCL™ for OpenCL™ in a Nutshell
Luke Iwanski, Games Technology Programmer @ Codeplay !SIGGRAPH Vancouver 2014
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SYCL for OpenCL in a nutshell
• Why?
• Where in the OpenCL ecosystem?
• Motivation
• Features overview
• Example time
• Roadmap
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• 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
Why SYCL?
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Device X Device Y Device Z
Alternative Language for
Kernels
SPIR Generator (e.g. Khronos patched Clang
open source on GitHUB)
Alternative Language for
Kernels
Alternative Language for
Kernels
High-level FrameworksHigh-level
FrameworksApps and Frameworks
!OpenCL Runtime
SPIR Standard Portable
Intermediate Representation SPIR 1.2 Released
January 2014
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
OpenCL ecosystemOpenCL C Kernel
Source
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OpenCL
SYCL for OpenCL
C++ template libraries
User application code
The layering of SYCL: Building an ecosystem
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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 innovations7
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SYCL features: Overview
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• 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 parallelism9
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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; " " }); " })); });
Task (nD-range)
WorkgroupWork item
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WorkgroupWork item
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Work item
WorkgroupWork item
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WorkgroupWork item
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Hierarchical Data Parallelism
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
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Example time: Simple kernel
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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
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Example time: Templated kernel
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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!!
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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
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• 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
SYCL roadmap
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SYCL Useful Links
• SYCL spec and forums:
• http://www.khronos.org/opencl/sycl
• triSYCL github:
• https://github.com/amd/triSYCL
• Codeplay’s blogs:
• http://www.codeplay.com/portal/
• Examples github
• https://github.com/codeplaysoftware/Siggraph14.git21
© Copyright Khronos Group 2014
Luke Iwanski
@liwanski_
Thanks!
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