The problem has 70K DOFs. The simulation was performed in a Dell laptop which has a Intel core i5 430m processor. According to the Intel site, this processor has the following specifications;
# of Cores 2 # of Threads 4 Processor Base Frequency 2.26 GHz Max Turbo Frequency 2.53 GHz Cache 3 MB SmartCache Bus Speed 2.5 GT/s DMI It seems that this processor actually has 2 cores. Thank you Pasha On Thursday, December 1, 2016 at 7:17:26 PM UTC+3:30, Wolfgang Bangerth wrote: > > > > I wrote a code using deal.II. Now, I want to compare effect of the > number of > > cores on the simulation time. The code is developed based on step-42 > from > > deal.II tutorial. > > > > The code is executed in Ubuntu 14.04, Intel core i5 and 4GB ram as, > > > > mpirun –n <number of cores> ./code parameter_file.prm > > > > The obtained results for 1, 2 and 4 cores is, > > > > Number of cores | Total wall clock time > > > > 1 | 1.22s > > > > 2 | 0.90s > > > > 4 | 0.93s > > > > > > Why the wall clock time for 4 cores is greater than the one obtained > with 2 cores. > > > > > > I also executed step-42 (Just 2 cycles) and the same pattern is > observed, > > > > Number of cores | Total wall clock time > > > > 1 | 4.73s > > > > 2 | 4.13s > > > > 4 | 5.89s > > There are multiple possibilities: > > * The problem is too small. If you split it into too many chunks, then > each > process does not have enough time to work, and all time is spent on > communication. Because you have more communication if you have more > processors, things actually take longer. Solution: Make the problem > larger. > > * You don't actually have four independent processors. For example, it > could > be that your i5 really only has two cores, each of which can execute two > threads concurrently. But these two threads compete for resources, and so > using 4 threads is not faster than using 2 threads (= 2 processes). > > Other possibilities come to mind as well, but these I would investigate. > > Best > W. > > > -- > ------------------------------------------------------------------------ > Wolfgang Bangerth email: bang...@colostate.edu > <javascript:> > www: http://www.math.colostate.edu/~bangerth/ > > -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
