GMRES performance

[Barry Smith]

On Oct 20, 2009, at 9:52 AM, jarunan at ascomp.ch wrote:

> Hello,
>
> I would like to know some information about GMRES performance in  
> PETSc if you have any experience.
>
> I am running a parallel test case(9300 cells) comparing cpu time  
> using by solvers in Petsc. While BICGSTAB was doing 0.9 sec, GMRES  
> 15 sec with the same preconditioner(Additive Schwarz). I did not  
> expect that GMRES would be that much slower. Everything is default.

    You need much more information than runtimes of the two cases to  
understand why one is faster than the other.
>
> Please share your experiences, how the performance of solvers are in  
> your test cases. Which option I should set to improve GMRES  
> performance? Is there the best combination of Preconditioner and  
> solver?

    Run both (with debugging turned off, hence optimized) using the  
option -log_summary and look at where each is code is spending its  
time. You can also see how many iterations (MatMult) each solver is  
requiring. Feel free to send the -log_summary output to petsc-maint at mcs.anl.gov 
  if you do not understand it.

    Barry

>
> Thank you very much
> Jarunan
>
> -- 
> Jarunan Panyasantisuk
> Development Engineer
> ASCOMP GmbH, Technoparkstr. 1
> CH-8005 Zurich, Switzerland
> Phone : +41 44 445 4072
> Fax   : +41 44 445 4075
> E-mail: jarunan at ascomp.ch
> www.ascomp.ch