Initial experience on openCL pragamming and develop GPU

solver for OpenFoam

Presented by: Qingfeng Xia

School of MACEUniversity of Manchester

Date: 2011-05-21

Structure

• Part 1. Introduction to OpenCL tools• coding, analyzing, debugging and profiling tools

• ViennaCL C++ template library for BLAS1, 2,3

• Part 2. Introduction to OpenFoam• Summary of GPU plugins

• Part 3. Profiling results• 3.1profiling ViennaCL blas library

• 3.2 profiling OpenFoam with GPU plugins• Future work: real-time PIV and DSMC solver

AMD APP kernel analyzer and profiler

• Command line tool: sprofile32 for Linux• Gui tool is a plugin for Visual Studio 2008/2010,

Professional version is needed

AMD APP kernel analyzer

AMD APP Profiler

Nvidia visual profiler (cross-platfrom)

gDEBbuger(cross-platform)

• (1)Powerful tool for openGL debugging and profiling, now available for openCL

• (2) Cross-GPU platform:• Support Nvidia and AMD GPU• (3) Cross-OS: windows and Linux Mac

• Cons: Too powerful to quick get work

IDE for C++ development (codelite)

• Cross-platform IDE

viennaCL : openCL c++ blas lib

• Brilliant lib, BLAS I,II, III

• Same API with Boost::ublas, can fall back to CPU

• However, this lib can not been linked with OpenFoam (Error: Segment fault)

Part 2

Introduction to OpenFoam (CFD)

Installation: (hope your GPU support double precision)

http://www.openfoam.org/archive/2.1.0/download/git.php

2.1 Quick Introduction to OpenFoam

• Free Computional Fluid Dynamics(CFD)

• (1) OpenFoam is programmed in C++, without an GUI frontend.

• (2)Code_saturne (finite volume) programmed in Fortran, has GUI front end

GPU solvers for OpenFoam

• (1) OF plugin for OpenFoam (before 2010)• Only free for single precision

• (2) Ofgpm package (GPL, May 2011)• from Symscape.com, Which transplant

OpenFoam from *nix to windows and develop a GUI(Cadium) for OpenFoam

• No preconditioner is implemented,• No benchmark is done

My work : clUtils, clFoam, vclFoam

(1) clUtils

• Just as practice of openCL programming, and provide utility for clFoam solver.

• Mainly in C, so there is no template suport,

• Single precision and double precision is switchable via Macro #define scalar float

(2)clFoam(PCG & PBiCG)

• (1) parallel the CPU serial code to parallel code in openCL, all preconditioners of Openfoam are usable

• (2) my own PCG and Bistab solver implented according to algorithms of textbook.

(3)vclFoam

• Wrappers to call ViennalCL sparse matrix solving utility.

• No preconditioner is implemented.

• Yet, do not work until now (gcc 4.4 openfoam 1.7)

Part 3: profiling

• (1) Tricks on the profiling

Profiling method of ViennaCL

Vector adding via ViennaCL

SpeedIT classic PCG solver

• A Japanese research has already make an profiling

• The result show the PCG on GPU is 3 time slower than CPU.

clFoam profiliing

Profiling platform

• Redqueen.rcs.manchester.ac.uk

• CPU AMD core 4, 2.3 GHz

• using one core on the cluster node

• GPU: Telsa C2050

Conclusion

• (1)Looks promising, peak Gflops is hundreds times higher than single CPU.

• (2)But not powerful enough to boost CFD simulation now.

• Domain decomposition is still the most effective way.

Future work

• (1) Real-time PIV vectoring processing up to 10 Hz.

• Most of calculation time is spent on Inter?? between 32X32pixels spots. it can make the best usage of the fast local cache on GPU.

• (2) Direct simulation Monte Carlo method: particles tracking,etc.

Acknowledgement

• RCS Dr Mike Bane, Dr. Simon, etc.

• Test on Nvidia GPU of the cluster Redqueen