[petsc-users] Why the code needs much longer time when I use MPI

[Barry Smith]

   What is the output of -ksp_monitor -ksp_view

  Barry

> On Sep 29, 2016, at 3:56 AM, Ji Zhang <gotofd at gmail.com> wrote:
> 
> Dear all, 
> I'm using KSP included in PETSc to solve some linear equations. The code runs well if I do not use mpirun. However, the running duration since increase linearly with the number of CUPs. 
> 
> The solve method is gmres and without precondition method. For a same case, it need about 4.9s with 'mpirun -n 1', which is about 7.9s if I use 'mpirun -n 2', and 12.5s when I use 'mpirun -n 4'. It looks like that I need double time when I use double CUPs. Is there any one could give me some suggestion? Thanks. 
> 
> Best, 
> Regards, 
> Zhang Ji, PhD student
> Beijing Computational Science Research Center 
> Zhongguancun Software Park II, No. 10 Dongbeiwang West Road, Haidian District, Beijing 100193, China