scaling in 4-core machine

[jarunan at ascomp.ch]

>> I run the test on a quad core machine with mpiexec -n 1, 2 and 4 to see
>> the parallel scaling. The cpu times of the test are:
>>
>> Solver/Precond/Sub_Precond
>>
>> gmres/bjacobi/ilu
>>
>> -n 1, 1917.5730 sec,
>> -n 2, 1699.9490 sec, efficiency = 56.40%
>> -n 4, 1661.6810 sec, efficiency = 28.86%
>>
>> bicgstab/asm/ilu
>>
>> -n 1, 1800.8380 sec,
>> -n 2, 1415.0170 sec, efficiency = 63.63%
>> -n 4, 1119.3480 sec, efficiency = 40.22%
>
> These numbers are worthless without at least knowing iteration counts.

I cannot show the iteration counts as I run it 50 time steps, 10  
maximum iterations for each time step, and 200 number of sweep (or  
maxit in KSPSetTolerance())

I test also our inhouse solver on the same machine, which is much  
slower than Petsc solver but scales better.

-n 1, 10022.8360 sec,
-n 2,  5684.1490 sec, efficiency = 88%
-n 4,  4067.0480 sec, efficiency = 61.61%

efficiency = 100*Speedup/nproc
Speedup = (cpu's time of -n 1)/(cpu's time of nproc)

If anyone has done parallel scaling test, it would be very kind, if  
you could share the test results.


Regards,
Jarunan