Hello, I profiled my application with cProfiler. Below is an excerpt from the resulting report: Fri Jan 04 01:07:39 2008 profiling_data_cProfile 15123197 function calls (14579262 primitive calls) in 228.517 CPU seconds Ordered by: internal time List reduced from 2933 to 50 due to restriction <50> ncalls tottime percall cumtime percall filename:lineno(function) 138305 135.419 0.001 135.817 0.001 {select.select} 26168 13.159 0.001 14.044 0.001 Sources\Server\Plugins\RKSimulation.py:218(UpdatePhysics) As you can see select.select takes up ~136 of ~229 seconds. This is the most expensive function. The row below shows the next expensive function which is one of my own. Now I am wondering whether a) the select calls are really taking up that much time (more than 50%!) b) if they are taking up that much time I'd like to find out how to reduce their execution time (either by minimizing the number it gets called or the time it takes to execute etc) My application doesn't invoke select.select itself so it is most likely called within twisted. I am on Windows and using the default reactor ("from twisted.internet import reactor"). -Matthias