Hello, thank you all very much for your replies.
I tried to simplify things and make the two versions as comparable as possible. I put the C++ part of the program into a shared object libff.so. For the exe the main function is linked against this shared object. For the python stuff I made an interface consiting of only one function call_solver with the same code that has the main function used for the exe. Then I created a wrapper for this interface using swig and linked interface.o, ff_warp.o and libff.so into _ff.so. The Python code just imports _ff and calls call_solver wich creates an object of the class Solver and calls its member solve (the main function of the exe does the same). I included some code for timing into the C++-code. #include <time.h> //beginning of solve clock_t t0 = clock(); ... clock_t t1 = clock(); //end of solve cout << "time used = " << (t1-t0)/CLOCKS_PER_SEC << endl; I'm using gcc4.5 (latest snapshot) and Python2.6 under Suse 10.3. The sources are compiled using the flags -fPIC -O3. Timing: 1) time python ff.py time used = 3.74 real 0m3.234s user 0m3.712s sys 0m0.192s 2) time ff time used = 2.19 real 0m3.170s user 0m2.088s sys 0m0.168s I tried some other optimizations: -O0: 1) time used = 21.91 real 0m21.568s user 0m22.001s sys 0m0.160s 2) time used = 20.87 real 0m22.206s user 0m20.989s sys 0m0.148s -O1 1) time used = 4.04 real 0m3.660s user 0m4.000s sys 0m0.160s 2) time used = 2.72 real 0m3.454s user 0m2.648s sys 0m0.164s It seems that there is an overhead of about 2 secs within the C++-code. I'm going to try this out with a problem that takes much more time than the present one. Regards Rolf Carl Banks wrote: > On Jun 23, 7:20 am, Rolf Wester <rolf.wes...@ilt.fraunhofer.de> wrote: >> Philip Semanchuk wrote: >> >>> On Jun 23, 2009, at 9:51 AM, Rolf Wester wrote: >>>> Hi, >>>> I have a C++ program that I would like to steer using Python. I made the >>>> wrapper using swig and linked the code (without the main function) into >>>> a shared object. My Python script loads the extension and calls a >>>> function of the C-extension, the rest runs entirely within the >>>> C-extension. For comparison I compiled the code including the main >>>> function with the same compilation options and linked all into an exe. >>>> The main function of the exe calls the same function as my Python script >>>> does. Surprisingly the code in the Python C-extension runs twice as long >>>> as the same code in the exe. Does anyone know what could be the reason >>>> for this behaviour? >>> If the runtime of the C/C++ code is short, the time spent initializing >>> the Python interpreter might have a big impact on the runtime of the >>> Python version. >> The runtime is about 2.5 sec and 5.0 sec respectively. I not only use >> the time command to measure the time consumed but I also measure the >> time within the C-code using clock() and get similar result. So the >> Python startup time is not the reason for the runtime difference I >> found. Thank you anyway. > > We can't really help you much unless you give us more details about > what you did (how did you built it, how did you time it, and how are > you calling the C extension from Python). All we can do is throw out > possible ideas, and I will toss out a few, but if that's not it you'll > have to post details. > > Are you building the extension with the same optimization flags as the > compiler? > > Are you calling the C code repeatedly from inside a Python loop? > -- http://mail.python.org/mailman/listinfo/python-list
