At 11:36 AM 5/3/2006, Chuck Swiger wrote:
Marc G. Fournier wrote:
In 4.x, it was a 'shut it off' sort of deal .. my new amd64 don't
appear to have it enabled, but my older i386 server that I just
upgraded to 6.x does:
user pid %cpu %mem vsz rss tt state start time command
root 14 104.0 0.0 0 8 ?? RL 11:38AM 0:55.02 [idle: cpu0]
root 11 99.1 0.0 0 8 ?? RL 11:38AM 0:00.00 [idle: cpu3]
root 13 99.1 0.0 0 8 ?? RL 11:38AM 0:00.00 [idle: cpu1]
root 12 98.0 0.0 0 8 ?? RL 11:38AM 0:54.54 [idle: cpu2]
Is it still something that I should disable, and, if so, how in 6.x?
You should test it for the workloads you have, but most of the time,
HT isn't especially helpful. AMD64 CPUs come in dual-core format
rather than HT-enabled. If you've seen "HT" or "HTT" applied to an
AMD system, it's likely an abbreviation for "HyperTransport" or
"HyperTransport Technology".
An Intel technical rep that gave a presentation on upcoming Intel VT
technology in processors (Virtualization Technology) that I attended
indicated that Hyperthreading was really designed to start getting
programmers to program threading into their applications in
preparation of dual core processors that we now have. Hyperthreading
will likely be removed in future processors now that dual core
technology is standard. In some instances it created a slight
performance boost.
Hyperthreading is known to hurt performance under high loads because
it diminishes the amount of cache available for each thread. Many
times, having no Hyperthreading but more CPU cache available
increases performance under high loads.
I typically disable Hyperthreading on all my servers as they are dual
processor or dual core/dual processor or better anyway. I tend to get
better results (with my applications) without Hyperthreading. I've
been experimenting with leaving it on with my workstation as it's not
a dual core or dual processor.
The reason hyperthreading frowned upon in multiuser scenarios of
FreeBSD is due to a vulnerability found in Hyperthreading:
http://lists.freebsd.org/pipermail/freebsd-security/2005-May/002903.html
Hyperthreading needs to be disabled in the BIOS. Often is referred to
as a "Virtual Processor" in the BIOS.
Vinny Abello
Network Engineer
Server Management
[EMAIL PROTECTED]
(973)300-9211 x 125
(973)940-6125 (Direct)
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Tellurian Networks - The Ultimate Internet Connection
http://www.tellurian.com (888)TELLURIAN
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fear" -- Mark Twain
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