# HyperThreading on or off?



## newtekie1 (Sep 26, 2010)

Something I noticed in my IntelBurnTest compilation thread was that the i7/i5/i3 CPUs seem to crunch numbers a heck of a lot better with HyperThreading off, and IntelBurnTest is multithreaded.

So with bigadv work units, do they go faster with HT off also?


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## FordGT90Concept (Sep 26, 2010)

Keep it on.  Multithreaded performance dropped by over 60% with hyperthreading off in my testing (all cores loaded to 100%).  The reason being is that 8 > 4.  Each work unit gets done a little slower but it is working on twice as many simutaneously.


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## Flibolito (Sep 26, 2010)

Yup. +1


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## newtekie1 (Sep 26, 2010)

FordGT90Concept said:


> Keep it on.  Multithreaded performance dropped by over 60% with hyperthreading off in my testing (all cores loaded to 100%).  The reason being is that 8 > 4.  Each work unit gets done a little slower but it is working on twice as many simutaneously.



Your comment doesn't make sense then.  If each unit gets done a little slower, that means lower PPD, no?

Like I said, in my number crunching tests with IntelBurnTest to see the actual GFLOPS my i7 and i3 were capable of, turning Hyperthreading off improved performance.  Reason being is that there is an inefficiency introduced with swapping out the registers and cache in the cores to switch between two threads.

I guess I'll test myself.


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## pantherx12 (Sep 26, 2010)

Depends on the program being used, it's a shame hyper threading isn't a dynamic process and only switches on when you need lots of threads.


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## DRDNA (Sep 26, 2010)

Leave it on on the I series processors unless your overclock is causing to much HEAT.


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## qubit (Sep 26, 2010)

Newtekie, I remember when I used to do SETI@Home pre-BOINC. I had an Athlon 3200+ (actually an o/c 2500+) and it would crunch units at a certain rate. Remember, these were single core 32-bit processors back then. <nostalgic moment>

I then got a P4 Northwood with HT. Run the same seti with HT off and it was a bit slower than the Athlon. But switch HT on and it would race past the Athlon at about twice the speed! It was awesome. 

What happened, is that switching on HT slightly reduced the speed of each individual seti unit, but then it did two of them simultaneously, which more than made up for it. It's a similar principle to how nvidia's GTX295 was faster than a GTX285 by using slower cores in SLI mode to make it faster overall than the 285.

So, in your case, just see which setting gives you more completed work units in unit time and leave it there. Each case is different and the advantage with HT on or off depends on the details.


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## kg4icg (Sep 26, 2010)

Anytime you are folding with a I3/I5/I7, leave hyperthreading on. Your folding does get accomplised quicker than if it was turned off.


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## hat (Sep 26, 2010)

Definately keep it on.


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## BUCK NASTY (Sep 26, 2010)

hat said:


> Definately keep it on.



+1. Leave it on. When folding -bigadv work units, the 4 physical & 4 virtual cores trick the work unit into thinking it is a dual-quad rig(8 cores). Otherwise, the work unit would not run for a normal quad. Core i7 rigs must be clocked to approx 3.6Ghz+ to meet the bonus deadline for -bigadv(which is substantial). Most of us run them @ 3.7 to 4.1ghz depending on thermal solutions for the CPU.


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## hat (Sep 26, 2010)

3.8GHz is supposed to be the sweet spot for i7s.


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## theonedub (Sep 26, 2010)

BUCK NASTY said:


> +1. Leave it on. When folding -bigadv work units, the 4 physical & 4 virtual cores trick the work unit into thinking it is a dual-quad rig(8 cores). Otherwise, the work unit would not run for a normal quad. Core i7 rigs must be clocked to approx 3.6Ghz+ to meet the bonus deadline for -bigadv(which is substantial). Most of us run them @ 3.7 to 4.1ghz depending on thermal solutions for the CPU.



I was hoping someone would have mentioned you can't run bigadv WUs on an i7 Quad without HT on


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## FordGT90Concept (Sep 26, 2010)

qubit said:


> I then got a P4 Northwood with HT. Run the same seti with HT off and it was a bit slower than the Athlon. But switch HT on and it would race past the Athlon at about twice the speed! It was awesome.


I saw the same results with my benchmarking app.  i7 w/o HT is a cripple.


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## kg4icg (Sep 26, 2010)

Actually, you can run the bigadv wu's on I7's at 3.2 ghz and still get the bonus, and more if it is a 2685 wu.


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## newtekie1 (Sep 26, 2010)

Well I kicked off hyperthreading and the time per frame went up by 6 minutes, which was enough to make me loose the points bonus deadline.



BUCK NASTY said:


> +1. Leave it on. When folding -bigadv work units, the 4 physical & 4 virtual cores trick the work unit into thinking it is a dual-quad rig(8 cores). Otherwise, the work unit would not run for a normal quad. Core i7 rigs must be clocked to approx 3.6Ghz+ to meet the bonus deadline for -bigadv(which is substantial). Most of us run them @ 3.7 to 4.1ghz depending on thermal solutions for the CPU.



Mines at 3.6GHz, but I might bump it up, but my TRUE is already struggling at 3.6GHz, with temps in the 70-72°C range when folding.



theonedub said:


> I was hoping someone would have mentioned you can't run bigadv WUs on an i7 Quad without HT on



I didn't have a problem.  I just had to have it download with HT on, then turn it off.


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## marvelous211 (Sep 26, 2010)

I leave mine on.  then again i have i3


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## overclocking101 (Sep 27, 2010)

with f@h wcg etc etc as long as they are multi threaded apps you will get much higher PPD with HT ON. yes each wu goes about 30% slower but the number of wu's being crunched t one time makes up for and then some. i tested this out when i first got my i7 860. its much much more ppd


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## newtekie1 (Sep 27, 2010)

overclocking101 said:


> with f@h wcg etc etc as long as they are multi threaded apps you will get much higher PPD with HT ON. *yes each wu goes about 30% slower but the number of wu's being crunched t one time makes up for and then some.* i tested this out when i first got my i7 860. its much much more ppd



With F@H that is definitely not true.  With SMP folding you are working on one WU at a time.  But yes, the single WU does seem to go faster with HT on according to my testing, and the WU actually does complete faster.


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## theonedub (Sep 27, 2010)

I think OC101's comment about multiple WUs applies to WCG.


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## newtekie1 (Sep 27, 2010)

theonedub said:


> I think OC101's comment about multiple WUs applies to WCG.



Yeah, I know that is how WCG works, but I was just correcting the F@H part.


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## [Ion] (Sep 29, 2010)

Definitely on 

Off, I get ~9-10k PPD @ 3,83ghz, on I can get 15-16k @ same clocks!


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