Re: Multithreading question

[Matteo Morini]

Jason Alexander wrote:

> > I did go multithread by scheduling the independent steps like this 
> > (untested pseudocode follows :-)
> > I'm going by memory... sorry for errors)
> >
> > [modelActions createActionForEach: agentsList message(step1)]
> > [modelActions createActionForEach: agentsList message(step2)]
>
>
> You might want to check if making the following change speeds things 
> up at all.  Instead of writing
>
> [modelActions createActionForEach: agentsList message(step1)]
> [modelActions createActionForEach: agentsList message(step2)]
>
> put
>
> [modelActions createAction: self message(fooBar)]
>
> (the right message might not be createAction... it's been a long time 
> since I've used Swarm)
>
> and then in the class file define fooBar as follows:
>
> - (void) fooBar() {
>   // loop over agentsList using standard iterator techniques, calling 
> step1 for each
>   // loop over agentsList using standard iterator techniques, calling 
> step2 for each
> }
>
> Introducing the above change into my code sped up one model by a 
> factor of 10.  Of course, in my case the slowdown was due to Swarm's 
> message-passing methods in createActionForEach when the list contains 
> heterogeneous agents.  In your case, I would guess the forks(), etc. 
> are much more of a bottleneck than Swarm's message-passing methods.
>
> Cheers,
>
> Jason

Thanks a lot for your advice: it's probably true that in my case the 
real bottleneck is not Swarm's expensive way of passing messages to the 
members of the list (uhm, a 10x speedup of your code? I think I need to 
check that createActionForEach CPU-eater more closely, in Swarm's 
source); still it looks a really neat trick that might help save many 
CPU cycles in those cases when one, after prototyping in Swarm, doesn't 
feel like restarting from scratch in C++ or Fortran or whatever, as Glen 
suggested.

---Matteo

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