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4486 posts

Uber Geek
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Topic # 62417 6-Jun-2010 19:19
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I have been reading on the net that hyperthreading can degrade performance. At the moment, I have disabled HT on my 930. I need it disabled so that I can overclock higher. Running the processor with HT on will increase my load temperature up to 10-15c more. I have also experienced occasional slight delay with games when the HT was on.

Quote from AMD BLOG with regards to hyperthreading:

Simultaneous Multithreading (SMT) is a method for squeezing two threads into one core. SMT was first researched by IBM in 1968 and introduced to x86 processors by Intel in 2002 under the name of HyperThreading. That sounds great, in concept. Carpooling is more efficient than giving everyone their own car, right?

Well, car pooling falls apart if the two employees live too far from each other and the office is close. If Bob lives 3 miles north of the office and Mary lives 2 miles south of the office, it really doesn’t make sense for them to carpool. In the bike and rider example above, think of SMT as a tandem bike. Yes it can move two riders, but not as quickly or efficiently as two separate bikes.

Can anyone here share their experience with regards to HT? Is HT really useless for servers?

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469 posts

Ultimate Geek
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  Reply # 339463 8-Jun-2010 17:45
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HT in it's first Intel go (pentium 4) was fairly useless - it had too many bottlenecks (parts of the CPU) that resulted in both threads being slowed down.

HT in Nehalem works much better, IF your using software that requires the use of 4 or more threads. I'm thinking video encoding, virtualisation or a particularly heavily used webserver.

As a case in point, I use my 920 pretty heavily for Folding@home, with HT on, I get a significantly higher performance output (using all 8 threads) than I do using just 4 with HT off. It's not double the performance, but it is more like 30% higher. That's at 3.8Ghz and currently holding ~60degC at 100%. I'm using a Noctua heatsink with push-pull fans. It's not that loud either.

Folding@home is actually a bit of a undersell for HT, because it tends to hit the HT bottlenecks harder than it does the rest of the CPU, so in some cases you can actually get well above a 30% boost.

Therefore, if you use between 4 and 8 threads on a frequent basis then you'd need an OC of 30% over and above your HT stable rate.


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