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Bobsk8

Hyperthreading

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Does P3D use hyperthreading, in other words would an i7 run P3D better than an i% because of the hyperthreading capability? 

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It is not a matter of "using HT" but getting increased performance with HT.

 

I believe it "uses" HT, just like FSX does, but most users get little to no value

out of that capability.

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You are better off leaving HT-OFF and raising your overclock. For example you may overclock to 4.6 but with HT- ON with the increased heat you may only get 4.3/4.4 stable.

 

I had a 2600k that would be happy all day @ 4.8, so I left HT- Off as I saw no difference with any testing I tried. But if you already have an i-7 go ahead and try it, see what works for you.

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Unlike FSX, you should be able to see benefits in terrain paging with HT on (and potentially improved smoothness).

 

See what overclock you can push to with HT enabled, and give it a try on and off. 

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You are better off leaving HT-OFF and raising your overclock. For example you may overclock to 4.6 but with HT- ON with the increased heat you may only get 4.3/4.4 stable.

 

I had a 2600k that would be happy all day @ 4.8, so I left HT- Off as I saw no difference with any testing I tried. But if you already have an i-7 go ahead and try it, see what works for you.

 

I believe this wisdom hasn't applied to the Haswell line (and assuming the Skylake line as well), but did apply to everything Sandy/Ivy-Bridge.

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I thought FSX has not been coded to use HT if so P3D should be the same. Here is a quote from another site.

 

 "Intel Hyper Threading: FSX has no code to recognize or process logical core hyper thread. I don't know how many times I have read some 'guru' has come up with an assessment that FSX will make use of or runs better with hyper thread enabled. This person really needs a sign! The REAL terrain 'guru' Adam from Aces as well as Phil Taylor specified years ago that FSX does not support any logical core threading (hyper thread).
 
The reason you SEE logical core activity in the Windows CPU monitor window is because the physical cache is used for each logical (hyper thread) core. "logical" core means there is no 'physical' hardware core but the hardware cache in use is there, and, FSX is DUMB so a thread is spawned due to the physical cache in use, but the data is never processed and used by FSX!"

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The HT is invisible to both FSX and P3d. FSX is only weakly multithreaded and only accesses a limited number of cores, whether physical or virtual. P3d will access as many cores as are available. For example, I have a dual Xeon system, with each processor having 6 physical  cores. I run with HT off, because there is no real advantage to HT, but with HT on, P3d uses all 24 "cores". It really doesn't help performance that much, because in P3d most of the CPU cores only load scenery.

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FSX doesn't "use hyperthreading" and knows nothing about it, neither does P3D. In a nutshell, HT increases the efficiency of thread swapping on a core. It comes with a price, 2 logical processors per core sharing the throughput of that core. Because of that some apps may spawn threads that start up on LPs shared by the same core and so compete on that core for maximum throughput. Apps that might do that can be helped to avoid it with an Affinity Mask that moves on the next starting thread to the next core by blocking an LP of the first core. Some apps, FSX-SE for example, spawn threads that don't compete on an HT enabled system and don't need an AM. FSX and P3D spawn upwards of 40 threads, from the use of a multitude of system resources like networking and IO. HT enabled systems increase efficiency of handling many threads greatly, else it wouldn't exist. However, with the cost of extra HT hardware on chip, in terms of heat, there may be a trade off with HT disabled when looking for ultimate GHz. Even though FSX doesn't use HT, it's running on a system that can find benefit from HT and can improve performance of the sim overall.
 

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HT should always be off to allow for the highest, stable overclock unless an application specifically will use it. A higher overclock will always yield better performance in P3D/FSX because more processor cycles means more work can get done. HT allows for better multi-tasking but ultimately no matter how many threads exist, the processor can only do so much per cycle - HT doesn't change performance the same increasing the amount of memory doesn't.

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As Prepar3D moves further and further away from being CPU bound... this thread's posts are a plentitude of misinformation. Prepar3D v2.x and most especially v2.5 do extremely well with HT enabled.

 

This isn't FSX. Using FSX as an explanation for anything when discussing Prepar3D is of little value.

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As Prepar3D moves further and further away from being CPU bound... this thread's posts are a plentitude of misinformation. Prepar3D v2.x and most especially v2.5 do extremely well with HT enabled.

 

This isn't FSX. Using FSX as an explanation for anything when discussing Prepar3D is of little value.

I am glad to know the P3D has been recoded  to use HT, maybe I  should give a try,  my system with HT would give 16 cores.

Unfortunately my FSX-SE causes my main PC to crash with HT enabled it doesn't like it at all.

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Actually it's probably your overclocking that's the source of the crash, but you probably don't want to hear that.

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As Prepar3D moves further and further away from being CPU bound... this thread's posts are a plentitude of misinformation. Prepar3D v2.x and most especially v2.5 do extremely well with HT enabled.

 

This isn't FSX. Using FSX as an explanation for anything when discussing Prepar3D is of little value.

+100.

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Actually it's probably your overclocking that's the source of the crash, but you probably don't want to hear that.

I do want to hear all the info I can get :smile:  I think is part of the fun to try new setting. my OC has been solid for a long time, HT + my FSX not so good. Very curious to see if P3D  would do in my system with HT enable. 

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So... OC is very stable... unless you have HT on and run FSX (which isn't HT aware). Willing to bet if you removed your OC... FSX would be stable with HT on.

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Patient: "Doc, it hurts when I do this."

Doc: "Don't do that. That will be $100."

 

:smile:

 

Vic
 

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So... OC is very stable... unless you have HT on and run FSX (which isn't HT aware). Willing to bet if you removed your OC... FSX would be stable with HT on.

Actually FSX will run with HT enable as long a set the AM to 8 cores, if I set to 16 will eventually freeze.  disabling OC on my system will defeat the purpose of having a system like mine, considering tha @ full load the temps never reaches beyond  50 c . Both of my PCs used to run FSX are OCed.

I also use my main PC for my work (AutoDesk Revit) and when is time to render the final I always enable HT as it takes several days to complete.

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Ah... yet another OC addict... it's so sad when we see them go before their time. :wink:

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Here I show how P3D v2.5 loses 8% throughput with no AM specified on a 6 core HT enabled system. In the lower half no AM (signified with AM=0) and a maxed LP 0 sharing core 0 with another P3D main thread on LP 1. In the upper half, LP 6 is hosting the main P3D thread with no other activity on LP 7 which shares throughput of core 3 with LP 6. In fact another process starts around 2/3 into the trace, whereby the jobscheduler efficiently distributes the work away from core 3.

AM3392AM0.jpg

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Also notable in the top half of the image we have the CPU partitioned off to three cores for all the threads spawned by the P3D process, and performs a few more fps better than the no AM setup. The AM 3392 was used as an example for test purposes, and a point of demonstration. In both examples above the maxed main thread can't go faster anyway, so allowing more secondary threads to interrupt it decreases performance still further. Therefore we prevent the ganging up of main threads on the primary core by masking one LP on the first core to be used, and when we have many LPs, we partition the CPU to disallow too many secondary threads forming which would stop the main thread too often to sync information.

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Steve you have shown time and again that HT works with P3D if people want to quote a guy talking about old code in FSX then sadly we need to inform people so they to don't get misinformation drummed into them.

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Thanks David. We can always mould an app to a machine, that is to use that machine efficiently, to it's best advantage. In the case of FSX-SE, that can clearly be seen placing its primary threads carefully and always shows an AM=0. No matter what we put in the jobsheduler cfg, FSX-SE does things the way it wants. Even with this kind of app though, its core affinity can be controlled by a hosting app if need be.

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No matter what we put in the jobsheduler cfg, FSX-SE does things the way it wants.

 

I have a dual core with HT on.

Here's FSX:SE with no affinitymask added in fsx.cfg. You can see it's only using logical core 2:

 

vMCUzgu.jpg

 

Now using affinitymask=5 (0101). It's using logical cores 0 and 2:

 

THoETjK.jpg

 

Finally, using affinitymask=15 (1111). It's using all 4 logical cores. In this case FSX:SE becomes noticeably more stuttery:

 

pP5trpI.jpg

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This is a discussion about Prepar3D, not FSX:SE.

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