Jim Perrin wrote: > On 6/7/06, Sam Drinkard <sam at wa4phy.net> 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/ > > > Thanks Jim. Those articles were enlightening to say the least. Time for more study on things! -- Sam W.Drinkard -- sam at wa4phy.net http://wa4phy.net Augusta Area Mesonet cell 706.825.8513 Home 706.868.7253 MAIL 4428 Branchwood Drive, Martinez Georgia, 30907-1304