Those variables would be...? Is this documented somewhere? If not, can
we get it documented?
OpenMP can do far more than just loop "unrolling", these days. Tasking
sections to run concurrent is also quite trivial. It can also offload to
GPU, etc. Check out the v4.5+ spec. It's pretty impressive. I believe it
can do most of what pthreads does, but you certainly lose control of
implementation details. Some compilers have an omp library while others
convert to pthreads.
I do find myself rewriting algorithms so that OpenMP can handle them. It
doesn't seem to handle nested loops with breaks very well and I'm not
entirely sure why.
On 10/9/2022 10:43 AM, William Hargrove wrote:
Can still run GRASS outside the shell by setting all of the
environment variables appropriately ...
OpenMP just works by "unrolling" all of the determinate loops, i.e.,
the ones that iterate a fixed number of times. No speedups to
anything else.
Speedup from OpenMP will be limited, depending on the number of
determinate loops present, and how much of the load they represent.
pthreads are totally flexible, but the programmer has to specify
everything, very carefully ...
But pthreads can speed up lots of stuff outside of determinate loops ...
HTH,
Bill H.
On 10/9/2022 12:37 PM, Brad ReDacted wrote:
Hello,
I'm working on adding parallelism to modules, but debugging is
turning out to be a logistical nightmare:
Why do I not get any reporting from GCC option
'-fsanitize=address|thread"?
I am also having trouble getting the profiler to work properly inside
GRASS (I assume due to shell?). The gmon.out file produced has no
usable data.
OpenMP is extremely poorly supported by most tools. valgrind with
helgrind reports a lot of nonsense. I can't seem to get the Intel
linux tools to work properly, either.
BTW, we are supporting both pthreads and OpenMP. While this isn't an
issue in most cases, there can be races and deadlocks if not handled
properly. Pthreads aren't entirely portable. OpenMP is. However,
pthreads gives us a more control. May I suggest using OpenMP for most
modules and reserve Pthreads to libraries, etc? Or should we start
moving away from pthreads?
Any suggestions would be greatly appreciated!
--
Best Regards,
-Brad
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