Etienne,
The main advantage of OpenMP is that you can compile the code with
(-fopenmp on gcc) or without OpenMP support but the output *should* stay
the same. So you can produce code that is highly optimized for
multithreaded environments (with little overhead) and still have
backwards compatibility for systems that lack threads.
When using OpenMP, you give up control when and how you create thread
contexts, this is managed at compile time (using the #pragma omp
directives (which btw should stay the only interface to OpenMP)). You
still have control of atomic sections, thread local/global variables and
so on.
I hope this explained a little.
Regards,
Fabian
On 06/11/2012 12:22 AM, Etienne Tourigny wrote:
Even - good stuff!
Can you comment on the usage of openmp for multi-threading? Is the
multi-threading in gdal entirely based on pthreads (in linux)?
It's my understanding that openmp is much easier to manage but offers
less fine-grained control - is that required for multi-thread warping?
Of course what works best is what is already working!
Sorry for such a generic question, I did not really look into the
specifics (other than a quick look at mutext handling).
Regards,
Etienne
On Sun, Jun 10, 2012 at 6:52 PM, Even Rouault
<even.roua...@mines-paris.org> wrote:
Le dimanche 10 juin 2012 23:44:54, Yogesh Dahiya a écrit :
As far I know gdal1.9 has integrated opencl so we can parallelize by
setting it right.
So what exactly is your addition.
By the way I tried opencl case and was able to get 16x over general case
for lanczos for image of 16000*16000
(Replying to list too, as others might have the same question)
Yes indeed, GDAL 1.9 can use OpenCL and this implementation is of course still
available.
Unfortunately, AFAIK, there is not yet any working OpenSource OpenCL
implementation (and my experience with some proprietary OpenCL implementation
has not always been convincing, like the GUI being totally unresponsive during
the processing).
The new multi-threaded implementation just uses traditional multi-threading
technics that are available on all platforms where GDAL can run.
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