[petsc-users] Number of unknowns/proc for scaling tests

[Casalegno Francesco]

Hello,


I am pretty new to PETSc and I would like to get some advice on choosing the right ratio of unknowns/proc.


I have implemented a finite element solver for 3D problems with potentially up to 5B vertices, using CG as iterative solver. To run weak scaling tests I have to keep constant the ratio unknowns/proc, but if that if this ratio is too small I will not see any scaling as the communication overhead would dominate. Similarly, for strong scaling tests I expect to observe nearly-linear scaling only up to a certain number of procs, after which communications will dominate.


My question is: what is a reasonable minimum number of unknowns per proc to get good scaling efficiency? I know that for <50k unknowns a direct solver would be preferable, but I do not know if this number is also a reasonable guess for the ratio unknown/proc.


Thanks in advance for your help!


Francesco
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20170227/ee0327a0/attachment.html>