In my experience hyperthreading can't really deliver two cores worth of processing simultaneously for processes expecting sole use of a core. Since you really have 512 cores I'm not surprised that you see a performance hit when requesting > 512 compute units. We should really get input from a hyperthreading expert, preferably form intel.
Doug Reeder On Oct 4, 2010, at 9:53 AM, Storm Zhang wrote: > We have 64 compute nodes which are dual qual-core and hyperthreaded CPUs. So > we have 1024 compute units shown in the ROCKS 5.3 system. I'm trying to > scatter an array from the master node to the compute nodes using mpiCC and > mpirun using C++. > > Here is my test: > > The array size is 18KB * Number of compute nodes and is scattered to the > compute nodes 5000 times repeatly. > > The average running time(seconds): > > 100 nodes: 170, > 400 nodes: 690, > 500 nodes: 855, > 600 nodes: 2550, > 700 nodes: 2720, > 800 nodes: 2900, > > There is a big jump of running time from 500 nodes to 600 nodes. Don't know > what's the problem. > Tried both in OMPI 1.3.2 and OMPI 1.4.2. Running time is a little faster for > all the tests in 1.4.2 but the jump still exists. > Tried using either Bcast function or simply Send/Recv which give very close > results. > Tried both in running it directly or using SGE and got the same results. > > The code and ompi_info are attached to this email. The direct running command > is : > /opt/openmpi/bin/mpirun --mca btl_tcp_if_include eth0 --machinefile > ../machines -np 600 scatttest > > The ifconfig of head node for eth0 is: > eth0 Link encap:Ethernet HWaddr 00:26:B9:56:8B:44 > inet addr:192.168.1.1 Bcast:192.168.1.255 Mask:255.255.255.0 > inet6 addr: fe80::226:b9ff:fe56:8b44/64 Scope:Link > UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 > RX packets:1096060373 errors:0 dropped:2512622 overruns:0 frame:0 > TX packets:513387679 errors:0 dropped:0 overruns:0 carrier:0 > collisions:0 txqueuelen:1000 > RX bytes:832328807459 (775.1 GiB) TX bytes:250824621959 (233.5 GiB) > Interrupt:106 Memory:d6000000-d6012800 > > A typical ifconfig of a compute node is: > eth0 Link encap:Ethernet HWaddr 00:21:9B:9A:15:AC > inet addr:192.168.1.253 Bcast:192.168.1.255 Mask:255.255.255.0 > inet6 addr: fe80::221:9bff:fe9a:15ac/64 Scope:Link > UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 > RX packets:362716422 errors:0 dropped:0 overruns:0 frame:0 > TX packets:349967746 errors:0 dropped:0 overruns:0 carrier:0 > collisions:0 txqueuelen:1000 > RX bytes:139699954685 (130.1 GiB) TX bytes:338207741480 (314.9 GiB) > Interrupt:82 Memory:d6000000-d6012800 > > > Does anyone help me out of this? It bothers me a lot. > > Thank you very much. > > Linbao > <scatttest.cpp><ompi_info>_______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users
