# 583L16 - EECS 583 Class 16 Research Topic 1 Automatic...

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EECS 583 – Class 16 Research Topic 1 Automatic Parallelization University of Michigan November 7, 2011

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- 1 - Announcements + Reading Material Midterm exam: Mon Nov 14 in class (Next Monday) » I will post 2 practice exams by tonight! » We‟ll talk more about the exam next class 1 st paper review due today! » Copy file to andrew.eecs.umich.edu:/y/submit » Put uniquename_classXX.txt Today‟s class reading » “Revisiting the Sequential Programming Model for Multi-Core,” M. J. Bridges, N. Vachharajani, Y. Zhang, T. Jablin, and D. I. August, Proc 40th IEEE/ACM International Symposium on Microarchitecture , December 2007. Next class reading » “Automatic Thread Extraction with Decoupled Software Pipelining,” G. Ottoni, R. Rangan, A. Stoler, and D. I. August, Proceedings of the 38th IEEE/ACM International Symposium on Microarchitecture , Nov. 2005.
- 2 - Class Problem from Last Time – Answer 1: y = 2: x = y 3: = x 6: y = 7: z = 8: x = 9: = y 10: = z 4: y = 5: = y 10 90 1 1 99 do a 2-coloring compute cost matrix draw interference graph color graph LR1(x) = {2,3,4,5,6,7,8,9} LR2(y) = {1,2} LR3(y) = {4,5,6,7,8,9} LR4(z) = {3,4,5,6,7,8,9,10} 2 1 4 3 Interference graph 1 2 3 4 cost 201 2 210 91 nbors 3 1 2 2 c/n 67 2 105 45.5

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- 3 - Class Problem Answer (continued) 2 1 4 3 1. Remove all nodes degree < 2, remove node 2 1 4 3 2. Cannot remove any nodes, so choose node 4 to spill stack 2 1 3 3. Remove all nodes degree < 2, remove 1 and 3 stack 4 (spill) 2 stack 1 3 4 (spill) 2 4. Assign colors: 1 = red, 3 = blue, 4 = spill, 2 = blue
- 4 - Moore‟s Law Source: Intel/Wikipedia

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- 5 - Single-Threaded Performance Not Improving
- 6 - What about Parallel Programming? –or- What is Good About the Sequential Model? Sequential is easier » People think about programs sequentially » Simpler to write a sequential program Deterministic execution » Reproducing errors for debugging » Testing for correctness No concurrency bugs » Deadlock, livelock, atomicity violations » Locks are not composable Performance extraction » Sequential programs are portable Are parallel programs? Ask GPU developers » Performance debugging of sequential programs straight-forward

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- 7 - 1 10 100 1000 10000 100000 1000000 10000000 100000000 1971 1975 1979 1983 1987 1991 1995 1999 2003 Years Speedup Conclusion – Compilers not about performance!
- 8 - That isn't to say we are parallelizing arbitrary C code, that's a fool's errand! ” – Richard Lethin, Reservoir Labs Compiler can’t determine a tree from a graph…” – Burton Smith, MSR Compilers can’t determine dependences without type information. Even then…” Burton Smith Decades of automatic parallelization work has been a failure…” – James Larus, MSR “All that icky pointer chasing code. ..” – Tim Mattson, Intel What Do the Experts Say?

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A Step Back in Time: Old Skool Parallelization Are We Doomed?
- 10 - Parallelizing Loops In Scientific Applications for(i=1; i<=N; i++) // C a[i] = a[i] + 1; // X Scientific Codes (FORTRAN-like) Independent Multithreading (IMT) Example: DOALL parallelization 0 1 2 3 4 5 C:1 X:1 C:2 X:2 C:4 X:4 C:3 X:3 C:5 X:5 C:6 X:6

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## This note was uploaded on 12/26/2011 for the course EECS 583 taught by Professor Flinn during the Fall '08 term at University of Michigan.

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583L16 - EECS 583 Class 16 Research Topic 1 Automatic...

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