Talk given at FOSDEM 2008 to introduce how to program the Cell BE processor of the Playstation 3 under Linux.

1. Programming with Linux on the
Playstation3
FOSDEM 2008
olivier.grisel@ensta.org
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Architecture overview:
introducing the Cell BE
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Installing Linux
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SIMD programming in C/C++
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Asynchronous data transfer with
the DMA

2. Who am I
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Java / Python developer at Nuxeo (FOSS document
management server)
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Interested in Artificial Intelligence (and need fast
Support Vector Machines)
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Slides to be published at:
http://oliviergrisel.name

3. PS3 architecture overview
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CPU: IBM Cell/BE @ 3.2GHz
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218 GFLOPS
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Main RAM: 256MB XDR (64b@3.2GHz)
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GPU: Nvidia RSX
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1.8 TFLOPS (SP) / 356 GFLOPS programmable
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VRAM: 256MB GDDR3 (2x128b@700MHz)
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System Bus: 2.5 GB/s

4. The Cell Broadband Engine
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1 PPE core @ 3.2GHz
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64bit hyperthreaded
PowerPC
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512KB L2 cache
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8 SPE cores @ 3.2GHz
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128bit SIMD optimized
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256KB SRAM

5. PS3 Clusters
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Cheap cluster for
academic researchers
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Carolina State U. and
U. Massachusetts at D.
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8+1 cluster with ssh and
MPI

6. PS3 GRID Computing
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PS3GRID project
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based on BOINC
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30,000 atoms simulation
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Folding@Home
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1 PFLOPS with 800
TFLOPS from PS3s
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BlueGene == 280
TFLOPS

7. Linux on the PS3
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Lv1 Hypervisor shipped with the default firmware
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Partition utility in the Sony Game OS menu
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Choose your favorite distro:
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Install a ­powerpc64­smp or ­ps3 kernel
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Install gcc­spu + libspe2

8. Programming the Cell/BE in C
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Program the PPE as a chief conductor to spread the
numerical code to SPEs
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Use POSIX threads to start SPE subroutines in
parallel
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Use SPE intrinsics to perform vector instructions
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Eliminate branches as much as possible in SPE code
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Align your data to 16 bytes

9. Introduction to SIMD programming
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128 bits registers (SSE2, Altivec, SPE)
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2 x double
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4 x float
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4 x int
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introduce new vector types
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1 vector float operation == 4 float operations
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logical (and, or, cmp, ...), arithmetic (+, *, abs, ...),
shuffling

10. SIMD programming – the big picture

11. Not always SIMD­izable

12. SIMD programming with libspe2 and
gcc­spu
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#include <spu_intrinsics.h>
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avoid scalar types use:
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vector_float4
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vector_double2
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vector_char16 ...
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d = spu_and(a, b); e = spu_madd(a, b, c);
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spu­gcc pure_spe_prog.c ­o pure_spe_prog.elf

13. Branch elimination
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avoid branching (if / else)
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c = spu_sel(a, b, spu_cmpgt(a, d));

14. A sample SPE program
volatile union {
vec_float4 vec;
float part[4];
} sum;
float dot_product(const float* xp, const float* yp, const int size) {
sum.vec = (vec_float4) {0, 0, 0, 0};
vec_float4* xvp = (vec_float4*) xp;
vec_float4* yvp = (vec_float4*) yp;
vec_float4* xvp_end = xvp + size / 4;
while(__builtin_expect(xvp < xvp_end, 1)) {
sum.vec = spu_madd(*xvp, *yvp, sum.vec);
xvp++;
yvp++;
}
return sum.part[0] + sum.part[1] + sum.part[2] + sum.part[3];
}

15. DMA with the SPUs' Memory Flow
Controllers
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#include <spu_mfcio.h>
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mfc_get(&local_data, main_mem_data_ea,
sizeof(local_data), DMA_TAG, 0, 0);
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mfc_put(&local_data, main_mem_data_ea,
sizeof(&local_data), DMA_TAG, 0, 0);
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mfc_getb(&local_data, main_mem_data_ea,
sizeof(local_data), DMA_TAG, 0, 0);
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spu_mfcstat(MFC_TAG_UPDATE_ALL);

16. Double­buffering – the problem

17. Double­buffering – the big picture

18. Double­buffering with MFC
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1. SPU queues MFC GET to fill buffer #1
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2. SPU queues MFC GET to fill buffer #2
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3. SPU waits for buffer #1 to finish filling
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4. SPU processes buffer #1
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5. SPU queues MFC PUT back content of buffer #1
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6. SPU queues MFC GETB to refill buffer #1
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7. SPU waits for buffer #2 to finish filling
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8. SPU processes buffer #2 (...)

19. Some resources
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Cell BE Programming Tutorial (ibm.com 190 pages)
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IBM developerworks short programming tutorials
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Search for articles by Jonathan Barlett
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Barcelona Supercomputing Center (software)
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http://www.bsc.es/projects/deepcomputing/linuxoncell/
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PS3 programming workshops (videos)
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http://www.cc.gatech.edu/~bader/CellProgramming.html
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#ps3dev on freenode

20. Thanks, credits, licensing
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Most schemas from excellent GFDL 'd tutorial by
Geoff Levand (Sony Corp)
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http://www.kernel.org/pub/linux/kernel/people/geoff/cell
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Pictures and trade marks belong to their respective
owners (Sony, IBM, Universities, Folding@Home,
PS3GRID, ...)
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All remaining work is GFDL

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