Re: [fluid-dev] Parallelize rendering using openMP

[Tom M.]

I'm pretty much done implementing my ideas of an openMP parallelization. In 
short:  I was not able to beat the current implementation.

While a parallel logarithmic buffer reduction sounds nice indeed it has the 
huge disadvantage that there needs to be a barrier waiting for all threads to 
finish rendering before the reduction can start. Using the profiling interface 
where all voices just keep playing, this barrier is actually pretty minor. But 
for real midi files where voices start and stop unpredictably this barrier 
dominates everything. David actually did a very good job here by efficiently 
using thread idling times to mix in any finished buffers.

I had to get rid of those barriers using the nowait clause (which consequently 
breaks rendering) to be slightly faster. This convinced me that the current 
parallelization approach is the right way to go, even if it involves a lot 
manual thread handling. And the little synchronization done currently is 
absolutely neglectable compared to my approach.

So for now I'm withdrawing the idea of switching to openMP. Perhaps I'll 
investigate whether aligned memory accesses to allow auto-vectorization by the 
compiler turn out to be more beneficial.

Tom