Riccardo Lucchese wrote:
> Hi,
>
> I'm working on profiling squeak/etoys for the olpc project.
>
> It seems to me that bytecodes cases in the interpret function
> (in /platform/unix/src/vm/interp.c) are not ordered in respect to
> the probability of their execution.
>
> Here is a graph for reference (more games in Etoys have
> the same pattern):
> http://www.bodhidharma.info/instructions.pdf
>
> What I did so far is changing the `256 cases switch' statement to an array
> of function pointers like (*exec_bytecode_funcs)[bytecode_id](
> ...shared data... );
> The process was automated with a python script and that needed a little bit
> of code cleaning; after some testing I couldn't trigger any sort of
> bug in the new code.
>
>
> if we assume a constant time T both for the execution of every
> [if !(right_case) jump next_case] in the old code and for the
> function pointer dereference in the new code there is a 10000% gain
> for the task of calling the right action for a given bytecode
> (also given the distribution showed in the graph linked above).
>
> In my tests this is a 20/30% win over the interpret routine timings
> for different games
> in etoys.
>   

Is that 20/30 % overall speedup ? If so, it is great!

Karl
> I appreciate any comments on this work.
> Maybe it could be done better than this ?
>
> Thanks,
> Riccardo
>
>
>