[SciPy-Dev] GIL and gaussian filter

[Sturla Molden]

Matthias Kümmerer <matthias at matthias-k.org> wrote:

> Thus I wanted to ask whether it is possible to release the GIL inside the
> correlate function and make parallel filtering easier. I will be happy to help
> with this, if you can give me some hints where I have to search.

Possible, but not recommended. The way gaussian_filter is written, you
would have to release and re-aquire  the GIL for every axis in the ndimage.
This is an expensive operation. It is better ti keep everything in C or
Cython, so you can release the GIL only once. 

Two other comments:

- It is better to do the multi-threading inside the gaussian_filter
function. 

- It is possible to express a Gaussian filter as a recursive IIR filter,
which is much faster than convolution. Also it does not truncate the filter
kernel and the speed is not dependent on the kernel size.

Sturla