[Numpy-discussion] Performance problems with strided arrays in NumPy
oliphant at ee.byu.edu
Tue Apr 18 20:03:01 CDT 2006
faltet at xot.carabos.com wrote:
>I'm seeing some slowness in NumPy when dealing with strided arrays.
>numarray is dealing better with these situations, so I guess that
>something could be done in NumPy about this. Below are the situations
>that I've found up to now (maybe there are others). For the timings,
>I've used numpy 0.9.7.2278 and numarray 1.5.1.
The source of this slowness is the use in numarray of special-cases for
Apparently, it is *much* faster to do
((double *)dst) = ((double *)src)
when you have aligned data than it is to do
memmove(dst, src, sizeof(double))
This is a useful piece of knowledge to have for optimization. There may
be other optimizations like that already used by Numarray but still
needing to be adapted for NumPy.
I applied an optimization to take advantage of this when possible and
got a 10x speed-up in the 1-d case.
My timings for your benchmark with current SVN of NumPy are:
NumPy: [0.021701812744140625, 0.021739959716796875, 0.021548032760620117]
Numarray: [0.052516937255859375, 0.052685976028442383, 0.052355051040649414]
NumPy: [~0.09, ~0.09, ~0.09]
Numarray: [~0.05, ~0.05, ~0.05]
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