Hi Matt, Thanks for your feedback! Would you suggest me the command line to get the number of sub iterations?
Il Dom 5 Feb 2023, 20:14 Matthew Knepley <[email protected]> ha scritto: > On Sun, Feb 5, 2023 at 1:26 PM Edoardo alinovi <[email protected]> > wrote: > >> Hello Petsc's crew, >> >> I would like to ask for some support in setting up the fieldsplit >> preconditioner in order to obtain better performance. I have already found >> some posts on the topic and keep experimenting, but I would like to hear >> your opinion as experts :) >> >> I have my fancy CFD pressure based coupled solver already validated on >> some basic problems, so I am confident the matrix is OK. However, I am >> struggling a bit in finding performance. In my experiments, I have found >> out that *schur *is the best in terms of overall iteration count, but it >> takes ages to converge! Using additive or multiplicative looks a better >> call, but in some cases I get a very high number of iterations to converge >> (500+). >> >> I attach here the logs (ksp_view and log_view) for an example case of >> the flow past a 90deg T-junction, 285k cells on 4 procs. >> >> GMRES + fieldsplit and schur take 90s to converge with 4 iters. Do you >> see anything strange in the way ksp is set up? >> > > 1. You are using A11 as the preconditioning matrix for the Schur > complement. Do you expect this to be a good idea? > > 2. You are using BJacobi/ILU(0) for A00. Is this a good idea? > > 3. Do you know how many iterates you are using for the A00 solve and for > the Schur complement? Note that A00 gets solved for each iteration of the > Schur complement, so you would multiply those two together to get an idea > of the time. > > Once we see the number of subiterates, I think we can say something more. > > Thanks, > > Matt > > >> Thank you for the support as always! >> > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener > > https://www.cse.buffalo.edu/~knepley/ > <http://www.cse.buffalo.edu/~knepley/> >
