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A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions. Gang Ren Peng Wu David Padua University of Illinois IBM T.J. Watson Research University of Illinois Presented by Gang Ren. Vector Unit.

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A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

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  1. A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions Gang Ren Peng Wu David Padua University of Illinois IBM T.J. Watson Research University of Illinois Presented by Gang Ren

  2. Vector Unit Register File (xmm0~xmm7) 128bits 128bits 128bits Multimedia Extensions (MME) • Additions to accelerate multimedia applications • For general-purpose processors: • MAX(HP), VIS(Sun), AltiVec(Motorola/IBM/Apple), SSE(Intel) • For special-purpose processors: • PS2(SONY), Graphics Processing Unit(NVIDIA) • Use SIMD architecture Intel SSE2 16 chars 8 shorts 4 integers 2doubles 4 singles A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

  3. Programming Multimedia Extensions foo.c int a[16],b[16],c[16]; for(i=0; i<16; i++) c[i] = a[i] + b[i]; foo.intrinsic.c vectorint a[4],b[4],c[4]; for(i=0; i<4; i++) c[i] = vec_add(a[i], b[i]); MME Vectorizer Native Compiler foo.s movaps xmm0, XMMWORD PTR [eax] addps xmm0, XMMWORD PTR [edx] movaps XMMWORD PTR [ecx], xmm0 Multimedia Extensions Assembler & Linker a.out A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

  4. Motivation Scientific Applications Multimedia Applications Diff Traditional Vectorization MME Vectorization GAP Vector Processors Multimedia Extensions Diff A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

  5. Gaps From Architecture Scientific Applications Multimedia Applications Diff Traditional Vectorization MME Vectorization GAP Vector Processors Multimedia Extensions Diff A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

  6. MME vs. Vector Processor • Differences in memory unit • MME: No scatter/gather memory operations • MME: Only support aligned memory access • Differences in ISA • MME: Specialinstructions for media processing • Example: Saturated Operations • MME: Non-uniform support for different element types • SSE2: Max/min operations on 16-bit short integers for(i=0; i<8; i++) for(j=0; j<8; j++) s += a[i*8+j] * b[j*8+i]; A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

  7. Gaps From Applications Scientific Applications Multimedia Applications Diff Traditional Vectorization MME Vectorization GAP Vector Processors Multimedia Extensions Diff A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

  8. Berkeley Multimedia Workload • Evolves from MediaBench • 12 applications written in C/C++ • Audio compression: ADPCM,GSM,LAME,mpg123 • Image/video compression: DVJU,JPEG,MPEG2 • Graphics: POVray, Mesa,Doom • Others: Rsynth, Timidity • Where are the example codes from? • Important loops in core procedures ( >10% total ex. time) A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

  9. Where Are Gaps From? • Different programming styles • Pointer access • Manually unrolled loops • Mismatches between application and language • Integer promotion • Saturated operation • Different code patterns • Bit-wise operations • Lookup tables A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

  10. C Language Issues: Integer Promotion • Integer promotion • Forced by ANSI C semantics (ISO/IEC 9899:1999) • All char or short types are automatically promoted to integer type before conducting any arithmetic operations. • Fit traditional scalar architecture well • MME supports sub-word level parallelism • Integer promotion will waste computation bandwidth • How to eliminate unnecessary integer promotion? • Some analyses needed to ensure the same result for(i=0; i<1024; i++)for(j=0; j<1024; j++) dst[i,j]=src1[i,j]+src2[i,j]; A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

  11. C Language Issues: Saturated Operations /* From BMW/GSM */ ltmp=a+b; if(( (unsigned)ltmp – MIN_WORD ) > ( MAX_WORD - MIN_WORD )) if(ltmp>0) ltmp = MAX_WORD; else ltmp = MIN_WORD; for(i=0; i<1024; i++)for(j=0; j<1024; j++) { dst[i,j]=src1[i,j]+src2[i,j];if(dst[i,j] > 255) dst[i,j] = 255; if(dst[i,j] < 0 ) dst[i,j] = 0; } A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

  12. Code Pattern: Lookup Tables • To implement saturated operations • To replace expensive math function calls /* From BMW/Lame */ if (init==0) for (i=0;i<LUTABSIZE;i++) lutab[i]=pow(...);...for (i=0;i<l_end;i++) { temp=...; if (temp<1000.0) { ix[i]=lutab[(temp*10)]; }} A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

  13. Some Related Work • Compilation based on traditional vectorization • Cheong and Lam’s optimizer for VIS (Sun) • Krall and Lelait’s traditional vectorizer for VIS • Sreraman and Govindarajan’s vectorizer for MMX(Intel) • Aart’s intra-register vectorization for the Intel architecture • Other compilation techniques • Krall and Lelait’s “Vectorization by loop unrolling” • Larsen and Amarasinghe’s “Superword level parallelism” • Fisher and Dietz’s “SIMD-within-a-register” • Product compilers • VAST/AltiVec, CodePlay/VectorC, Intel compiler,… A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

  14. Conclusions • Gaps exist between traditional vectorization and compilation for multimedia extensions • From differences between two architectures • From different programming styles, mismatch with language semantics, different code patterns • Additional compiler techniques need to be developed or extended to bridge these gaps A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

  15. Future Work • Our first step to unleash the power of MMEs • Manual vectorization to see how far we can go • Implement our vectorizer on SUIF • Propose new techniques to bridge the gaps • Extend application domain • Traditional applications: SPECfp, SPECint • Applications for embedded systems A Preliminary Study On the Vectorization of Multimedia Applications for Multimedia Extensions

  16. Thank You

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