> On Sep 13, 2018, at 2:16 PM, Edoardo alinovi <[email protected]>
> wrote:
>
> Yes, I need it or at least I think so. I am using piso alghorithm which
> requires to solve the pressure eq twice in a time step. Since the coeffs of
> the matrix are different in the two cases, then I have to setup the pc every
> time.
What about at the next time-step? Are the coefficients different yet again
at each new timestep?
Barry
>
> Thanks Barry!
>
> Il gio 13 set 2018, 21:08 Smith, Barry F. <[email protected]> ha scritto:
>
>
> > On Sep 13, 2018, at 1:55 PM, Edoardo alinovi <[email protected]>
> > wrote:
> >
> > Hello Barry,
> >
> > Thank you very much for your replay! Maybe the best feature of PETSc is
> > this mailing list :) You are right cg + block Jcoby is twice faster than
> > hypre, but still a bit slower than OF. I have definitely to test a bigger
> > case. It seems that hypre loses a lot of time in setting up the PC. Is this
> > normal?
>
> Yes, BoomerAMG (or any AMG method) has "large" setup times that don't
> scale as well as the solve time. Thus if you can reuse the setup for multiple
> solves you gain a great deal. The best case is, of course, where the same
> Poisson problem (with a different right hand side obviously) has to be solved
> many times. I noticed in your log_view that it seems to need to do a new
> setup for each solve.
>
> Barry
>
> >
> > Thank you!
> >
> >
> >
> > ------
> >
> > Edoardo Alinovi, Ph.D.
> >
> > DICCA, Scuola Politecnica
> > Universita' di Genova
> > 1, via Montallegro
> > 16145 Genova, Italy
> >
> > email: [email protected]
> > Tel: +39 010 353 2540
> >
> >
> >
> > 2018-09-13 20:10 GMT+02:00 Smith, Barry F. <[email protected]>:
> >
> > What pressure solver is OpenFOAM using? Are you using the same
> > convergence tolerance for the pressure solver for the two approaches? Have
> > you tried PETSc with a simpler solver: -pc_type bjacobi or -pc_type asm ;
> > the problem is pretty small and maybe at this size hypre is overkill?
> >
> > Barry
> >
> >
> > > On Sep 13, 2018, at 12:58 PM, Edoardo alinovi <[email protected]>
> > > wrote:
> > >
> > > Hello PETSc's frieds,
> > >
> > > It is a couple of weeks that I am trying to enhance the perforamance of
> > > my code. Actually I am solving NS equation for a 3D problem of 220k cells
> > > with 4procs on my laptop (i7-7800k @ 2.3Ghz with dynamic overclocking). I
> > > have installed petsc under linux suse 15 in a virtual machine (I do not
> > > know if this is important or not).
> > >
> > > After some profiling, I can see that the bottle neck is inside KSPSolve
> > > while solving pressure equation (solved with cg + hypre pc). For this
> > > reason my code is running twice time slower than openFOAM and the gap is
> > > only due the solution of pressure. Have you got some hints for me? At
> > > this point I am sure I am doing something wrong! I have attached the log
> > > of a test simulation.
> > >
> > > Thank you very much!
> > >
> > > ------
> > >
> > > Edoardo Alinovi, Ph.D.
> > >
> > > DICCA, Scuola Politecnica
> > > Universita' di Genova
> > > 1, via Montallegro
> > > 16145 Genova, Italy
> > >
> > > email: [email protected]
> > > Tel: +39 010 353 2540
> > >
> > >
> > > <run_log_view.txt>
> >
> >
>
