making python computations fast
TRANSCRIPT
Copyright © 2015 Russel Winder 1
Making Python computations fast
Dr Russel Winder
email: [email protected]: @russel_winder
Web: http://www.russel.org.uk
Copyright © 2015 Russel Winder 2
Presentation slots arevery short…
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Structure
BeginningMiddleEnd
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What is the value of ? π
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π
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It's simples. Александр Орлов 2009
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The Maths
The equation:
Leads to the approximation formula:
∑i=0
n 4
(1+xi2)Δ x≈π
∫0
1 4
(1+x2)dx=π ¿
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The ConceptionCalculate an approximation to the area undera conic section by filling the area with a knownnumber of rectangles of known size and thensum the areas of the rectangles.
The narrower the rectangles, the more accurate the approximation.
This is a data parallel problem andembarrassingly parallel.
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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 tobe done on different processors.This should make things faster.
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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
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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.
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It is all just too slow.
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More Code● Use Cython.● Use Numba.
cf. lightning talk at PyConUK 2014.
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A lot faster but… iscontrolling parallelism inPython the thing to do…
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Even More Code● Use NumPy.● Use C.● Use C++/Boost.● Use D/PyD.● Use Chapel/PyChapel.
Offload the whole computation,Leaving Python code as thecoordination 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/
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Parallelism and computationis not Python's forte.
(Even though Python is a great language.)
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So do not do it.
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NUMA
PGAS
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Employ a multilingual,polyglot programming mentality.
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Making Python computations fast
Dr Russel Winder
email: [email protected]: @russel_winder
Web: http://www.russel.org.uk
Copyright © 2015 Russel Winder 21
John, you were a truly Pythonic hero,I miss your physical presence here.