Calcimage faster with hyperthreading disabled

[Philipp Poeml]

I have something interesting here. I am testing my new i7 PfE PC and was doing some calculations. Unfortunately PfE is using only 1 core for everyting it does, so I figured, what happens if I switch of "hyperthreading", which is supposed to make computers faster? In the internet I learned that it should have no effect to switch it off because the modern hyperthreading is cool and is managing cores and threads very well.

I calculated the same calcimage project, once with hyperthreading on, once off. Result:
hyperthreading on: 19.5 minutes
hyperthreading off: 12.5 minutes

So there IS a difference. Amazing!

Now I am wondering if I should switch it off everywhere else too, because I don't really have applicatoins that use it. However on the laptop I have only 2 cores, i.e. 4 virtual ones with hyperthreading on. Since also Win7 64 bit is using some, and there I run more applications next to PfE I might leave it on there.

Will test.

[John Donovan]

I have something interesting here. I am testing my new i7 PfE PC and was doing some calculations. Unfortunately PfE is using only 1 core for everyting it does, so I figured, what happens if I switch of "hyperthreading", which is supposed to make computers faster? In the internet I learned that it should have no effect to switch it off because the modern hyperthreading is cool and is managing cores and threads very well.

I calculated the same calcimage project, once with hyperthreading on, once off. Result:
hyperthreading on: 19.5 minutes
hyperthreading off: 12.5 minutes

So there IS a difference. Amazing!

Now I am wondering if I should switch it off everywhere else too, because I don't really have applicatoins that use it. However on the laptop I have only 2 cores, i.e. 4 virtual ones with hyperthreading on. Since also Win7 64 bit is using some, and there I run more applications next to PfE I might leave it on there.

Will test.

Hi Philipp,
Interesting.

If I were you I would perform a "back to back" test.  Because the 2nd test might be quicker just because it was run 2nd- for example because of disk caching).

So maybe try this:

1. Run with hyper threading
2. Run without hyper threading
3. Run with hyper threading
4. Run without hyper threading

Are 1 and 3 similar?  Are 2 and 4 similar?  OK. Now which set is faster and by how much? Then calculate the variance of each set...     

[Philipp Poeml]

I could do multiple runs, yes.

However, on my computer the hyperthreading is switched off in the bios, which makes a restart necessary. So I don't think the 2nd test had any disk caching or anything. So before each test I made a fresh reboot of the system to have similar conditions.

[John Donovan]

I could do multiple runs, yes.

However, on my computer the hyperthreading is switched off in the bios, which makes a restart necessary. So I don't think the 2nd test had any disk caching or anything. So before each test I made a fresh reboot of the system to have similar conditions.

If each image calculation was performed just after a re-boot, the test as a whole should be good.  Still might be worth trying both a small image and also a large image and see if the effect is size independent. 

I'd be interested if anyone has an explanation for the calculation being faster without hyper threading.