i7 & hyperthreading

[Tullphan]

Am I right in assuming that to get a better overclock for an i7 920 that one must disable hyperthreading?
I'm running an i7 920 on a EX58-UD4P motherboard.
It'll do 3.8 w/no problems, but I can't seem to reach the magical 4.0ghz. Of course i'm sure those extra nanoseconds i'll be saving helps...hehehe.

 

[PAo_ReVoLT]

if you turn off HT, usually it will low your core temp about 10c

that is about it

 

[Tullphan]

Perhaps I just didn't get a "cream of the crop" chip.
How much of a performance hit will one take by disabling HT? Enough to really notice??

 

[chinesepiratefood]

Unless it somehow let you get to like 4.4ghz + I would just keep HT on

 

[86 5.0L]

no, not worth it

 

[rive22]

HT enabled provides in general a 30-50% gain. vs a 5% overclock gain for the last 200mhz

Have you tried upping vtt?

 

[drescherjm]

The question of HT on versus off really depends on if you want to run 4 threads or 8 threads. As a programmer I max out all 8 cores every day I use my i7 860 at work so HT is definitely on. If you never hit 4 cores at full load you probably want HT off.

 

[cyclone3d]

HT enabled provides in general a 30-50% gain. vs a 5% overclock gain for the last 200mhz

Have you tried upping vtt?

Although I leave HT on, I would very much like to know exactly where you get your 30-50% speed gain with HT on. If you are using some encoding program that is multithreaded and are using Windows 7, I highly suggest you look up turning off thread locking.

Try running IntelBurnTest with HT off or with only 4 threads instead of 8. It actually gives you a higher Gflops score and finishes faster with only 4 threads.

Even doing testing where I know more threads helps, doesn't give a 30% gain. A max gain of 20% is about all you will see under ideal circumstances... and more like 5-10% under normal circumstances.

 

[rive22]

Although I leave HT on, I would very much like to know exactly where you get your 30-50% speed gain with HT on. If you are using some encoding program that is multithreaded and are using Windows 7, I highly suggest you look up turning off thread locking.

Try running IntelBurnTest with HT off or with only 4 threads instead of 8. It actually gives you a higher Gflops score and finishes faster with only 4 threads.

Even doing testing where I know more threads helps, doesn't give a 30% gain. A max gain of 20% is about all you will see under ideal circumstances... and more like 5-10% under normal circumstances.

http://software.intel.com/en-us/art...t-effects-on-a-server-transactional-workload/

I get exactly a 50%+/- increase in actual output in my audio encoding alone with HT enabled on both my I3 and I7 machines. Not sure what's going on with you, but there's no way I'd ever turn HT off, ever. Video encoding is dramatically faster as well as system responsiveness while heavy multitasking.

And here is direct from intel site.

"Intel® Hyper-Threading Technology: Analysis of the HT Effects on a Server Transactional Workload". Highlights include the following key points:

* Performance improved 30% by enabling Intel HT Technology
* End user response time decreased from 50ms to 37ms.
* The average number of cycles to complete a transaction increased 49%.

 

[Tullphan]

HT enabled provides in general a 30-50% gain. vs a 5% overclock gain for the last 200mhz

Have you tried upping vtt?

I upped it, but I can't remember how much before I got disgusted & dropped it back down.
I also upped the vcore to 1.3, but that didn't help either.
Right now, i'm having to set the vcore to 1.28125 to get 3.8 linpack stable.

 

[Cecil]

HT adds about 20-30% ONLY in multi-threaded apps. And thats a best case number.
However, even at 3.8 with HT, you would never be able to tell a difference with daily stuff between that, and 4 or even 4.2 with or without HT. My i7 is way overkill at 4.4 with HT on, but temps arent in the way so why not

Its personal prefrence and depends on what you do. If you are playing games, watching movies, etc... basice daily stuff, you could turn it off to save on temps and stress.

 

[Tullphan]

Another question I have...just what, exactly, is "CPU PLL", "QPI", & "VTT"? And how do they affect overclocking?

 

[dnottis]

Well I've seen differing results. I use ConvertxtoDVD which will use 8 threads, however mine will encode faster with 4 threads than 8. Also, LinX will show 47 GFLops @ 4.0 with HT on and 57 GFlops @ 4.0 with HT off. The FSB is the same, so is memory. I either run 21 x 200 or 20 x 200.

Anyone have any idea why this is??

 

[dnottis]

Another question I have...just what, exactly, is "CPU PLL", "QPI", & "VTT"? And how do they affect overclocking?

Google. They all affect stability though. a good start would be 1.85 PLL, AUTO QPI and 1.30VTT

 

[Cecil]

There is no reason to ever touch PLL voltage unless you are running about 4.6+. Auto or stock 1.8 is fine for everything else.

 

[cyclone3d]

From what it sounds like with those specific apps that can supposedly gain 30-50% with HT on... there may be some not very efficient code in them... or they may have been written like that on purpose so that they can claim that much of a speedup.

Although they are able to use additional threads, it sounds like they have the threads broken up so one or more threads have to wait for another thread to finish what it is doing before it continues. In that case, HT is probably going to help more.

IF you have a multithreaded program that doesn't have to use things like locks, which is the best way to do it if you can, you will see a MAX of 20% speedup with HT on... and that is with almost perfect scaling.