gil_load

I looked into the GIL saturation as measured with gil_load (https://github.com/chrisjbillington/gil_load), but perhaps I should have included more numbers here. To me, seeing the GIL held for 40% of time and significant time spent waiting on GIL by other threads was a fairly strong indicator. Keen to hear your thoughts/experience on it.

This seems like a good place to spruik something I made, a Python package for profiling how much the GIL is held: https://github.com/chrisjbillington/gil_load In my experience, the GIL is not held for nearly as high a proportion of the time as people think it is, because properly written C extensions and blocking io always releases the GIL. So long as the proportion of time the GIL is held is not approaching 100%, then you can still get gains from threading. This is almost always the case in numerically heavy code that uses numpy or scipy, since the extensions release the GIL. Threads work almost just as well at speeding up this code as in any GIL-free interpreter. And usually long before you consider multithreaded code, you'll want to move the bottlenecks of your code over into Cython or something, since that can give speedup factors muc

This. Any part of my numerical code that is a bottleneck, is either already coming from scipy or numpy, or I'm going to write in Cython if possible. Rewriting in Cython is already the opimisation you would do before going to multithreaded, because it can get you factors of 10, 100, etc, whereas multithreaded gets me a factor of 4 to 8 depending on how many cores I have and how independent the workload is. So by the time it comes to consider multiple threads, the bottlenecks that I want to paralellise are already non-GIL-holding. I wrote a tool to measure what proportion of the time the GIL is held in a program: https://github.com/chrisjbillington/gil_load I encourange people to measure what fraction of the time the GIL is actually held in their multithreaded programs. Unless it's approaching 100%, go ahead and use more threads! You will g