no parallel speedup with slepc krylovschur

[Christian May]

On Tue, 30 Jun 2009, Toby D. Young wrote:

>
>> I want to solve the following generalized eigenvalue problem in parallel:
>>
>> However, when I use multiple CPUs, I cannot see any speedup. I am not sure
>> whether this is a problem of the matrix or of my system. Can anybody
>> please have a look?
>
> This goes against everything I have done with the KrylovSchur solver!
>
> Can you confirm (to yourself and to me) that your system really is using
> multiple processors and not multiple threads? If you can answer that I may
> take a look at your code. Show me some output please.
>

Sure, here's the output for 2 CPUs:

**************
Job <ompirun ./SPsolver3D-dune ini-files/fuhrer-dot/fuhrer-dot-test.ini 
-eps_type krylovschur -st_type sinvert -st_shift -0.228 -eps_ncv 32 
-eps_tol 1
e-10 -ksp_monitor -ksp_type gmres -pc_type bjacobi -ksp_rtol 1e-14 
-st_ksp_rtol 1e-14 -ksp_converged_reason> was submitted from host 
<brutus2> by user
  <cmay>.
Job was executed on host(s) <2*a6400>, in queue <beta.m>, as user <cmay>.
</cluster/home/phys/cmay> was used as the home directory.
</cluster/home/phys/cmay/SPsolver3D> was used as the working directory.
Started at Tue Jun 30 15:32:25 2009
Results reported at Tue Jun 30 15:49:58 2009

Your job looked like:

------------------------------------------------------------
# LSBATCH: User input
ompirun ./SPsolver3D-dune ini-files/fuhrer-dot/fuhrer-dot-test.ini 
-eps_type krylovschur -st_type sinvert -st_shift -0.228 -eps_ncv 32 
-eps_tol 1e-10
-ksp_monitor -ksp_type gmres -pc_type bjacobi -ksp_rtol 1e-14 -st_ksp_rtol 
1e-14 -ksp_converged_reason
------------------------------------------------------------

Successfully completed.

Resource usage summary:

     CPU time   :   2096.54 sec.
     Max Memory :      1831 MB
     Max Swap   :      2461 MB

     Max Processes  :         2
     Max Threads    :         2

The output (if any) follows:


*********************

On one CPU, the needed time is
slepc time:     262.43

On two CPUs, it is
slepc time:     247.88

> How do you invoke your code on the command line? mpicc???

I compile with mpiCC and run with ompirun.

Thanks
Christian

>
> Best,
> 	Toby
>
> -----
>
> Toby D. Young
> Philosopher-Physicist
> Adiunkt (Assistant Professor)
> Polish Academy of Sciences
> Warszawa, Polska
>
> www:   http://www.ippt.gov.pl/~tyoung
> skype: stenografia
>

---------------------------------------------------------------------------
Christian May

ETH Zurich
Institute for Theoretical Physics, HIT K 31.5
CH-8093 Zurich, Switzerland

Tel: + 41 44 633 79 61
Fax: + 41 44 633 11 15

Email: cmay at itp.phys.ethz.ch