(Not sure if this list or OCR-discuss would be better, but I suspect there's very
little difference in readership at the moment)
I've been starting to look into OCR as a framework for future research,
and wrote a parallel mergesort in order to learn how to code with EDTs. I also did some
performance analysis, which is in the attached slides. Given how new OCR is, the OCR
version of mergesort was impressively close to a pthreads version as long as I didn't
try to use tasks that were too small, and managed to beat the pthreads version in some
cases. It's a promising start, particularly given that mergesort is a good program
for a pthreads-style implementation (very regular, only log2(num processes) barriers).
One thing that turned up in the analysis is that there's fairly high
malloc/free overhead in OCR programs. Based on the examples, my code was calling malloc
twice per EDT I spawned, and it looks like OCR is calling malloc/free a fair amount
internally. Not surprisingly, the overhead really starts to show up when you try to use
very fine-grained tasks.
As an experiment, I tried using Google's tcmalloc instead of the base
malloc/free that came with my Linux distributions, and there were some significant
improvements. For extremely fine-grained tasks, performance improved by greater than 20x.
For more reasonable task sizes, the impact of task size on performance got much smaller
with tcmalloc. Tcmalloc didn't help much for the larger task sizes, which isn't
At any rate, I thought I'd share the results with everyone and see if
it starts some discussion.