1. MUDA
MUltiple Data Accelerator language
Project Overview
Feb 24, 2008
Syoyo FUJITA

2. ?

3. Nikkei 225 index

4. ?

5. GPU slumps
CPU soars
Geforce 9800 GX2 rumor
1 TFlops?( 3x of G80)
500 GFlops? (+50% of G80)
?
No
update !
PS3 Mac Pro octa
179.2 Gflops
+800 %
204 Gflops
2007 Feb/2008

6. Nikkei 225 index

7. Subprime shock!
Nikkei 225 index Credit boom ends!
US economy declines!
Green IT!
Future of GPU trend

8. Accelerated
computing
many-core GPGPU
CPU GPU

9. Accelerated
computing
many-core GPGPU
NO!
CPU GPU
GPGPU was dead!!
GPU will be dead soon!!

10. Why GPU -> GPGPU is
BAD
• Larger latency : host <-> PCI-ex
• Internal architecture is black box
• Only GPU maker knows it
• Larger cost of branching
• Debugger?
• Program only runs on specific GPU maker’s
GPU
• Not portable.

11. Why CPU -> Accelerated computing is
GOOD
• Easy to program
• CPU maker provides good internal spec
documentation
• Fast execution of branching
• gdb :-)
• Portable & Versatile

12. Accelerated
computing
many-core
MUDA
CPU

13. MUDA’s goal
• Withdraw CPU’s maximum
floating point performance for
large data
• SIMD
• Cache optimized computation

14. MUDA example
MUDA code
vec sqrtmu(vec x)
{
vec y0, y0x, y0xhalf;
vec oneish = bit(0x3f800001);
y0 = rsqrt(x);
y0x = y0 * x;
y0xhalf = 0.5 * y0x;
return ((oneish - y0 * y0x) * y0xhalf + y0x);
}

15. __m128 sqrtmu (const __m128 * x)
{
x86/SSE output
__m128 y0 ;
__m128 y0x ;
__m128 y0xhalf ;
const __m128 t_vec4 = (__m128)_mm_set1_epi32( 1065353217) ;
__m128 oneish = t_vec4 ;
const __m128 t_vec6 = (*x) ;
const __m128 t_vec5 = _mm_rsqrt_ps( t_vec6) ;
y0 = t_vec5 ;
const __m128 t_vec8 = y0 ;
const __m128 t_vec9 = (*x) ;
const __m128 t_vec7 = _mm_mul_ps( t_vec8 , t_vec9 ) ;
y0x = t_vec7 ;
const float t_float13 = 0.5 ;
const float t_float12 = t_float13 ;
const __m128 t_vec10 = _mm_set_ps1( t_float12 ) ;
const __m128 t_vec14 = y0x ;
const __m128 t_vec11 = _mm_mul_ps( t_vec10 , t_vec14 ) ;
y0xhalf = t_vec11 ;
const __m128 t_vec19 = oneish ;
const __m128 t_vec20 = y0 ;
const __m128 t_vec21 = y0x ;
const __m128 t_vec15 = _mm_mul_ps( t_vec20 , t_vec21 ) ;
const __m128 t_vec16 = _mm_sub_ps( t_vec19 , t_vec15 ) ;
const __m128 t_vec22 = y0xhalf ;
const __m128 t_vec17 = _mm_mul_ps( t_vec16 , t_vec22 ) ;
const __m128 t_vec23 = y0x ;
const __m128 t_vec18 = _mm_add_ps( t_vec17 , t_vec23 ) ;
return t_vec18 ;
}

16. Why MUDA?

17. No unified way to
describe SIMD op
• SSE: _mm_add_ps()
• AltiVec: vec_add
• SPE: spu_add

18. CPU ISA changes
frequently
• SSE2(2000), SSE3(2004), SSE4(2006)
• SSE5 and Coming New CPU design(?)
• 8-element SIMD?, no SIMD in the future
CPU?
• Keeping up with them is hard and
not productive. Waste of your
time.

19. SSE2 C code
SSE4 C code
MUDA
MUDA
compiler
VMX C code
Portable,
CPU independent
description
LLVM IR
CPU or Arch dependent
code

20. Status
• SSE2 backend : 75 %
• SSE4 backend : 0 %
• VMX backend : 20 %
• LLVM IR backend : 30 %
• SIMD math function for MUDA : 5 %
• Automatic optimizer : TODO
= I’m currently working on

21. Future direction
• Cache miss analysis and memory access
optimization
• Valgrind, Cache Miss Equation(CME)
• Automatic optimization
• Such like FFTW, ATLAS and Spiral are doing
• Automatic error measurement for
floating point computation
• Interval Arithmetic, Affine Arithmetic, Gappa

22. Performance gap
100
75
Better
50
Scalar:SIMD cache miss:cache hit
25
= =
1:4 1:100
0
SIMD Memory

23. Performance gap
100
Optimizing memory access is much
75
more important than SIMDization
Better
50
Scalar:SIMD cache miss:cache hit
25
= =
1:4 1:100
0
SIMD Memory