On 3/27/07, Fawzi Mohamed
I decided to cleanup my program by splitting it in different modules. As I was curious about the cost of splitting it, or dually the efficiency of the intermodule optimization I timed it before and after the split. These are the results (ghc-6.6.20070129 on Linux AMD64):
Original: 3 Modules with the computational one with an export list
real 0m0.385s user 0m0.378s sys 0m0.003s time:100%
Variant 1: split computational module in 6 submodules without export list, kept computational module reexporting the stuff with an export list
real 0m0.467s user 0m0.464s sys 0m0.003s time: 122%
Variant 2: like Variant 1 but removing the old computational module (no reexport list) 134% real 0m0.513s user 0m0.506s sys 0m0.003s
All the functions in my modules have type specialized signatures, so non-specialization should almost never be an issue. The module with the Main function was not the exported one.
So 20% speed hit, I had hoped for 0, but it is not unbearable (even if my code has to be as fast as possible, this was a very short run), probably I will keep it split to have cleaner code. Not I will have to write an export list for each module a see it the things improve, and how much. If someone has an idea on how else I can improve timings please tell me.
For starters, I'd question whether those results are statistically significant; your program doesn't run for very long. 20% of less than .5 seconds is short enough that the 20% hit you're seeing could be affected by random noise. If there's a way to adjust the input to your program so that it runs for more than a few seconds, you may want to see what results you get that way. Even so, intuitively I'd also expect to see a performance hit when splitting a program into multiple modules, as GHC's optimizer is designed with separate compilation as a consideration. As always, you probably need to do profiling in order to figure whether it's worth bothering about. Cheers, Tim -- Tim Chevalier * chevalier@alum.wellesley.edu * Often in error, never in doubt Confused? See http://catamorphism.org/transition.html