I have done several simulation runs linked with ParaView Catalyst for in-situ 
visualization on Titan with 18k cores and have the following 
observations/questions hoping to seek input from this list.


1.       It appears IceT-based image compositing for 18k cores takes such a 
long time that it becomes unpractical to output images in-situ. Specifically, 
in our case, it takes about 14 minutes for coprocessing for one time point that 
output a composited image while simulation alone for one time point only takes 
about 7 seconds. I have also done a simulation run with in-situ visualization 
on Titan with 64 cores on a much lower resolution mesh (10 million element mesh 
as opposed on 167 million element mesh for 18k core run), in which case 
coprocessing with image output for 64 cores takes about 25 seconds. Question: 
is there any way to improve performance of image compositing for 18k cores for 
in-situ visualization?

2.       I also tried to avoid image output, but output polydata extracts using 
XMLPPolyDataWriter instead on 18k cores. In this case, in-situ coprocessing 
only takes about 20 seconds (compared to 14 minutes with image output). 
However, too many files are generated to a point that breaks the hard limit on 
maximal number of files in a directory since the parallel writer writes a vtp 
file from each of 18k cores. So the output data files have to be broken up into 
different directories. However, I got "cannot find file" error when I put a 
directory name as a parameter in coprocessor.CreateWriter() function call in my 
python script. I tried initially to put "data/vorticity_%t.pvtp" as a 
parameter, but it fails with "cannot find file" error. Not sure whether this is 
a bug or I need to put absolute full path in rather than a relative path to the 
current directory. Another question is whether there are ways to composite 
these files generated from different cores into one single file while doing 
coprocessing so only one composite file is generated rather than a huge number 
of files when running on large number of cores.

Thanks for any input, suggestions, and comments!

Regards,
Hong
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