[Libmesh-users] Performance of libmesh and PETSC in a linux cluster

[Min Xu <mi...@sc...>]

Hi,

In an attempt to test the performance of libmesh and petsc in a linux cluster, 
a 2D time-dependent diffusion equation is solved on a uniform mesh of size 
320x320 and the solution is performed on 74 time steps.

In the first case, 5 processors are used. The diffusion system is:
 EquationSystems
  n_systems()=1
   System "Diffusion"
    Type "TransientLinearImplicit"
    Variables="u"
    Finite Element Types="LAGRANGE"
    Approximation Orders="FIRST"
    n_dofs()=103041
    n_local_dofs()=20850
    n_constrained_dofs()=0
    n_vectors()=3

The assembling takes 4.8251s for one time step and the total 74 petsc 
solutions takes  396.8s.

In the second case, total 10 processors are used. The diffusion system is:

 EquationSystems
  n_systems()=1
   System "Diffusion"
    Type "TransientLinearImplicit"
    Variables="u"
    Finite Element Types="LAGRANGE"
    Approximation Orders="FIRST"
    n_dofs()=103041
    n_local_dofs()=10378
    n_constrained_dofs()=0
    n_vectors()=3

The assembling takes 2.38s for one time step and the total 74 petsc solutions 
takes 208.2s.  

All the above times are active times.

This proves that both libmesh and petsc scales well with the number of 
processors. 

But one thing puzzles me most is the alive time reported is 1226.03s which is 
6 times of the petsc solution time. What does the extra time spent come from?
Anyone has some idea?

Best,

--Min