On Dec 22, 2010, at 9:55 AM, Yongjun Chen wrote: > > Satish, > > I have reconfigured the PETSC with ?download-mpich=1 and > ?with-device=ch3:sock. The results show that the speed up can now remain > increasing when computing cores increase from 1 to 16. However, the maximum > speed up is still only around 6.0 with 16 cores. The new log files can be > found in the attachment. > > > (1) > > I checked the configuration of the first server again. This server is a > shared-memory computer, with > > Processors: 4 CPUS * 4Cores/CPU, with each core 2500MHz > > Memories: 16 *2 GB DDR2 333 MHz, dual channel, data width 64 bit, so the > memory Bandwidth for 2 memories is 64/8*166*2*2=5.4GB/s.
Wait a minute. You have 16 cores that share 5.4 GB/s???? This is not enough for iterative solvers, in fact this is absolutely terrible for iterative solvers. You really want 5.4 GB/s PER core! This machine is absolutely inappropriate for iterative solvers. No package can give you good speedups on this machine. Barry > > It seems that each core can get 2.7GB/s memory bandwidth which can fulfill > the basic requirement for sparse iterative solvers. > > Is this correct? Does the shared-memory type of computer have no benefit for > PETSC when the memory bandwidth is limited? > > > (2) > > Beside, we would like to continue our work by employing a matrix partitioning > / reordering algorithm, such as Metis or ParMetis, to improve the speed up > performance of the program. (The current program works without any matrix > decomposition.) > > > Matt, as you said in > http://lists.mcs.anl.gov/pipermail/petsc-users/2007-January/001017.html > ,?Reordering a matrix can result in fewer iterations for an iterative solver?. > > Do you think the matrix partitioning/reordering will work for this program? > Or any further suggestions? > > > Any comments are very welcome! Thank you! > > > > > > > > > On Mon, Dec 20, 2010 at 11:04 PM, Satish Balay <balay at mcs.anl.gov> wrote: > On Mon, 20 Dec 2010, Yongjun Chen wrote: > > > Matt, Barry, thanks a lot for your reply! I will try mpich hydra firstly and > > see what I can get. > > hydra is just the process manager. > > Also --download-mpich uses a slightly older version - with > device=ch3:sock for portability and valgrind reasons [development] > > You might want to install latest mpich manually with the defaut > device=ch3:nemsis and recheck.. > > satish > > > > <log_ch3sock_jacobi_bicg_4cpus.txt><log_ch3sock_jacobi_bicg_8cpus.txt><log_ch3sock_jacobi_bicg_12cpus.txt><log_ch3sock_jacobi_bicg_16cpus.txt>
