On 6/7/06, Sam Drinkard <sam@xxxxxxxxxx> wrote:
Another question some of you may help me make decisions on. I've been doing some reading that indicates that having HT turned on in this dual xeon machine might actually slow down the computing process rather than speeding it up. I rebooted this a.m., and turned HT off, just prior to my main application run. One thing that might be of note, this application is using OMP for utilizing both cpu's, and prior to turning off HT, I had been running the software using 2 cpu's of the 4 that the OS sees. I'm waiting on a model run to finish to see if there is any appreciable difference, but the one thing I do notice right off is cpu utilization is running close to 100% on both, where before, it averaged maybe 50% or thereabouts. Again, sar is showing at last count, 83.56% utilization for user, 10.27% system and only 0.02% nice. Idle was 5.74%.
It's entirely possible that your system is lying about load when moving back and forth between HT and real SMP. Logical CPUS (HT) are nearly identical to physical CPUs as far as the operating system is concerned. Since you have half the number of CPUS with HT turned off, but you're still running the same amount of jobs, the load should be higher. Hopefully this page will explain that a little bit better. http://www.cognitive-dissonance.org/wiki/Load+Average Additionally as far as HT performance is concerned, I've only really found two pages that help, although the IBM load is a bit older and may not be accurate anymore. http://perfcap.blogspot.com/2005/05/performance-monitoring-with.html http://www-128.ibm.com/developerworks/linux/library/l-htl/
I'm attempting to squeeze every last bit of processing power out of this machine, and would entertain suggestions on tuning if there happen to be any types of tuning that would help.
For performance tuning, I usually start with the filesystem tweaks: mount ext3 noatime, and changing the commit time from 5 to 30 After that I move to /etc/sysctl.conf and tweak the kernel.shmmax, shmmin, shmall, and vdso values depending on the application I'm most concerned about, as well as fs.file-max.
From there I move to the I/O scheduler/elevator for the system. RH
magazine had a decent article about this. http://www.redhat.com/magazine/008jun05/features/schedulers/ -- This message has been double ROT13 encoded for security. Anyone other than the intended recipient attempting to decode this message will be in violation of the DMCA _______________________________________________ CentOS mailing list CentOS@xxxxxxxxxx http://lists.centos.org/mailman/listinfo/centos
