Intel Hyper Threading - on or off?

[TurboTomato 90]

There's been a lot of chat about affinity masks of late, and how we should set them, what values to use etc.

 

What doesn't seem to have been answered (at least not fully) is a step back from that - should we have hyperthreading turned on or off in the first instance? Can P3D make use of the additional cores, or does the overhead (which there must be, at least in terms of scheduling) mean that it's more trouble than it's worth? Does it differ between people's individual setups?

[hesynergy 67]

Yup!...we need more definitive info broken down into a comparitve spreadsheet detailing metrics and the efficacy of multiple cores, hyper threading, and P3D setup.

 

I have have a 2600 K with over-clocking to 4.5GHz/Gforce 770 2GB, which has served me well, but I haven't done any research into the usefulness of having four cores or hyper threading, or affinity mask.

 

Chas

[Sesquashtoo 2,846]

There's been a lot of chat about affinity masks of late, and how we should set them, what values to use etc.

 

What doesn't seem to have been answered (at least not fully) is a step back from that - should we have hyperthreading turned on or off in the first instance? Can P3D make use of the additional cores, or does the overhead (which there must be, at least in terms of scheduling) mean that it's more trouble than it's worth? Does it differ between people's individual setups?

I run v2.4 with it always on...(actually, all sims, all the time...) and can harvest usually 28-30 FPS in any given flight and taxi situation. That's on an Intel i7-975 Extreme CPU OC'ed to 4.02 Ghz

[pincopanco 5]

HT on, no affinity mask.

[Pe11e 812]

I run both sims (P3D2 & FSX) with HT on and AF=84.

 

cheers

[SteveW 1,792]

Since a core is going to task switch between processes anyway, the introduction of HT made it possible to increase the performance of task switching by emulating two Logical processors with one Core. So additional hardware on the chip increases the throughput of task switching when HT=On and we get doube the apparent LPs in with the bargain. So with HT=On we have to apply an AM like Pe11e (using an AM=84 we presume an 8LP CPU), to keep our main thread on a core to itself, hence eliminating task switching there anyway. But what about additional threads? Well we can double up secondary threads per core using HT to improve switching performance while pushing the core toward max. Given two identical threads that would max out the core would get 50% each, halving the performance of the core to each thread, that can become counter productive. What about other processes, networking is highly threaded and will benefit from HT=On for example. FSX/P3D don't particularly benefit themselves with HT=On since we try not to allow any task switching on the cores we allow the sim to use, but some system functionality might benefit. With HT=Off, some circuitry is disabled on the chip, and ultimately the chip can be overclocked higher with less heat.

[pincopanco 5]

AM=84...blurry assured.

[SteveW 1,792]

HT on, no affinity mask.

AM=84...blurry assured.

There are plenty of discussions about AMs, and it's a shame to blurt in with personal experiences. But on your comments, I would say your HT=On with no AM produces a result with the main thread, and one secondary thread on the first core together. This splits the performance between the main thread and the secondary thread on that core. This slows down the sim since the main thread needs full throughput, but gets less as it shares with texture loading. The increased throughput experienced with your AM=84, and your blurry textures, suggests the texture loading is slow. Perhaps you have modified your cfg to cause this? Else why not try an AM that keeps the main thread to a core of it's own as required, but also one that loads up several secondary threads to increase texture throughput, like AM=244, or AM=254.

[pincopanco 5]

If you just can not to do without an AM, then 85.

In P3D 2.x the core 0 must be enabled.

[Nyxx 6,993]

AM=84...blurry assured.

On your PC that might be, but please don't speak for everyone using that setting. Info like that is misleading.

[TurboTomato 90]

If you just can not to do without an AM, then 85.

In P3D 2.x the core 0 must be enabled.

 

That's confusing in itself - do you mean using an AM that ends xxxxxx11?

 

Anyway you've made an assumption that HT will be turned on (or you've got a 8 core processor), which is what the question is about, rather than 'what should the AM be?'.

[SteveW 1,792]

Still the confusion about AMs rages on.

 

We need an AM with FSX/P3D when

 

1) We have HT enabled. We want to keep the main thread to a core by itself, preventing a secondary simulator thread occupying the other LP on that same Core.

 

or

 

2) When we have many cores. We don't want too many secondary threads since they stop the main thread to communicate.

 

 

If you just can not to do without an AM, then 85.

See my point 1 above.

 

 

In P3D 2.x the core 0 must be enabled.

Incorrect. P3D can use any cores we choose.

 

 

Generally HT is set to disabled with aggressive Overclocking, but otherwise leave HT=On, and ensure the AM is well thought through, and tested.

[Pe11e 812]

 

 

Generally HT is set to disabled with aggressive Overclocking, but otherwise leave HT=On, and ensure the AM is well thought through, and tested.

 

Hmm, why? I oc'ed my i3770k to 4.5ghz, and kept HT on, never had any problems. Is this performance related or stability, or...?

[SteveW 1,792]

Many overclockers say that they see lower temps with HT=Off, and so can push the OC higher, so they say.

[Nyxx 6,993]

Steve,

It might be a good idea if you have time to do a guide with step by step SS were needed, it would be nice to put an end to all the misguiding posts around AM with HT, for once and all.

 

Just a thought Steve as XXX does not suit all. Pincopanco reply's are perfect e.g on how misguided it gets. Am sure they don't mean to but.....