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