[petsc-users] Investigate parallel code to improve parallelism

Barry Smith bsmith at mcs.anl.gov
Fri Feb 26 10:53:16 CST 2016

> On Feb 26, 2016, at 10:27 AM, TAY wee-beng <zonexo at gmail.com> wrote:
> On 26/2/2016 11:32 PM, Barry Smith wrote:
>>> On Feb 26, 2016, at 9:28 AM, TAY wee-beng <zonexo at gmail.com> wrote:
>>> Hi,
>>> I have got a 3D code. When I ran with 48 procs and 11 million cells, it runs for 83 min. When I ran with 96 procs and 22 million cells, it ran for 99 min.
>>    This is actually pretty good!
> But if I'm not wrong, if I increase the no. of cells, the parallelism will keep on decreasing. I hope it scales up to maybe 300 - 400 procs.
>>> So it's not that parallel. I want to find out which part of the code I need to improve. Also if PETsc and hypre is working well in parallel. What's the best way to do it?
>>   Run both with -log_summary and send the output for each case. This will show where the time is being spent and which parts are scaling less well.
>>    Barry
> That's only for the PETSc part, right? So for other parts of the code, including hypre part, I will not be able to find out. If so, what can I use to check these parts?

   You will still be able to see what percentage of the time is spent in hypre and if it increases with the problem size and how much. So the information will still be useful.


>>> I thought of doing profiling but if the code is optimized, I wonder if it still works well.
>>> -- 
>>> Thank you.
>>> Yours sincerely,
>>> TAY wee-beng

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