Making Python computations fast

Slides from my PyConUK 2015 session

Transcript

1. Copyright © 2015 Russel Winder 1 Making Python computations fast Dr Russel Winder email: russel@winder.org.uk twitter: @russel_winder Web: http://www.russel.org.uk
2. Copyright © 2015 Russel Winder 2 Presentation slots are very short…
3. Copyright © 2015 Russel Winder 3 Structure Beginning Middle End
4. Copyright © 2015 Russel Winder 4 What is the value of ? π
5. Copyright © 2015 Russel Winder 5 π
6. Copyright © 2015 Russel Winder 6 It's simples. Александр Орлов 2009
7. Copyright © 2007–2015 Russel Winder 7 The Maths The equation: Leads to the approximation formula: ∑ i=0 n 4 (1+x i 2) Δ x≈π ∫ 0 1 4 (1+x2) dx=π ¿
8. Copyright © 2007–2015 Russel Winder 8 The Conception Calculate an approximation to the area under a conic section by filling the area with a known number of rectangles of known size and then sum the areas of the rectangles. The narrower the rectangles, the more accurate the approximation. This is a data parallel problem and embarrassingly parallel.
9. Copyright © 2007–2015 Russel Winder 9 The Parallelism • Addition is commutative and associative so we can partition the overall summation in any way we want: a + b + c + d + e + f ( a + b ) + ( c + d ) + ( e + f ) Can partition the overall sum into bits to be done on different processors. This should make things faster.
10. Copyright © 2007–2015 Russel Winder 10 Adding the Parallelism • Instead of doing all the calculations sequentially, partition the problem into a number of chunks. problem subproblem result subproblem subproblem subproblem . . . scatter gather fork join reduce Data parallel map
11. Copyright © 2007–2015 Russel Winder 11 Some Code • Sequential. • Use threads to obtain parallelism…not. • Use process to obtain parallelism. Friends don't let friends use Python 2 instead of Python 3.
12. Copyright © 2007–2015 Russel Winder 12 It is all just too slow.
13. Copyright © 2007–2015 Russel Winder 13 More Code • Use Cython. • Use Numba. cf. lightning talk at PyConUK 2014.
14. Copyright © 2007–2015 Russel Winder 14 A lot faster but… is controlling parallelism in Python the thing to do…
15. Copyright © 2007–2015 Russel Winder 15 Even More Code • Use NumPy. • Use C. • Use C++/Boost. • Use D/PyD. • Use Chapel/PyChapel. Offload the whole computation, Leaving Python code as the coordination code. https://github.com/russel/Pi_Quadrature/tree/master/Python http://dlang.org/ http://pyd.readthedocs.org/ http://chapel.cray.com/ http://pychapel.readthedocs.org/
16. Copyright © 2007–2015 Russel Winder 16 Parallelism and computation is not Python's forte. (Even though Python is a great language.)
17. Copyright © 2007–2015 Russel Winder 17 So do not do it.
18. Copyright © 2007–2015 Russel Winder 18 NUMA PGAS
19. Copyright © 2007–2015 Russel Winder 19 Employ a multilingual, polyglot programming mentality.
20. Copyright © 2015 Russel Winder 20 Making Python computations fast Dr Russel Winder email: russel@winder.org.uk twitter: @russel_winder Web: http://www.russel.org.uk
21. Copyright © 2015 Russel Winder 21 John, you were a truly Pythonic hero, I miss your physical presence here.