as i perform a paralll running. I first run decomposePar (number of subdomains is defined to 8). After i run : mpi -np 8 renumberMesh -parallel. After i run : mpi -np 8 simpleFoam -parallel >log. I run to finish pyFoamPlotWatcher.py log to visualise real time residual.

I never used renumberMesh. Did you try to start the case without that?
How many CPU cores do you have? Did you try to use just 2 ?


I recommend to start a new thread with just that "execution time / clock time" problem since I can't help you and I doubt anyone else reads this thread...