[petsc-users] Performance of PETSc TS solver

[Barry Smith]

   Also always send the output from running with -log_summary whenever you ask performance questions so we know what kind of performance it is getting.

   Barry

On Aug 12, 2013, at 8:14 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> "Jin, Shuangshuang" <Shuangshuang.Jin at pnnl.gov> writes:
> 
>> Hello, PETSc developers,
>>        I have a question regarding the performance of PETSc TS solver
>>        expecially the TSTHETA. I used it to solve my DAE equations. 
> 
> TSTHETA is not L-stable and not stiffly accurate, so it's not normally
> something that you'd want to use for a DAE.  Make sure you're getting
> meaningful results and try switching to something like an ARKIMEX or
> ROSW since those are likely better for your problem.
> 
>>  I have recorded the solution times when different numbers of processors are used:
>> 
>> 2 processors: 1021 seconds,
>> 4 processors: 587.244 seconds,
>> 8 processors: 421.565 seconds,
>> 16 processors: 355.594 seconds,
>> 32 processors: 322.28 seconds,
>> 64 processors: 382.967 seconds.
>> 
>> It seems like with 32 processors, it reaches the best
>> performance. However, 322.28 seconds to solve such DAE equations is
>> too slow than I expected.
> 
> The number of equations (1152) is quite small, so I'm not surprised
> there is no further speedup.  Can you explain more about your equations?
> 
>> 
>> I have the following questions based on the above results:
>> 1.      Is this the usual DAE solving time in PETSc to for the problem with this dimension?
> 
> That depends what your function is.
> 
>> 2.      I was told that in TS, by default, ksp uses GMRES, and the
>> preconditioner is ILU(0), is there any other alterative ksp solver or
>> options I should use in the command line to solve the problem much
>> faster?
> 
> I would use -ksp_type preonly -pc_type lu for such small problems.  Is
> the system dense?
> 
>> 3.      Do you have any other suggestion for me to speed up the DAE computation in PETSc?
> 
> Can you describe what sort of problem you're dealing with, what causes
> the stiffness in your equations, what accuracy you want, etc.