scaling in 4-core machine

[jarunan at ascomp.ch]

Hello,

I have read the topic about performance of a machine with 2 dual-core  
chips, and it is written that with -np 2 it should scale the best. I  
would like to ask about 4-core machine.

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%

Why is the scaling so low, especially with option -n 4?
Would it be expected to be better running with real 4 CPU's instead of  
a quad core ship?



Regards,
Jarunan



-- 
Jarunan Panyasantisuk
Development Engineer
ASCOMP GmbH, Technoparkstr. 1
CH-8005 Zurich, Switzerland
Phone : +41 44 445 4072
Fax   : +41 44 445 4075
E-mail: jarunan at ascomp.ch
www.ascomp.ch