With HT off, look at the use of the cores in task manager. Often we see 50% or more, possibly 100% on the first core then up to 40% on the second core and so on. So if we then enable HT look again at the use of each logical processor (LP). With 100% on the first LP (primary task) and 40% on the second LP (secondary task) that's two tasks on the two virtualised LPs of the first core - meaning that core is over taxed, doing more work than we want. By making the first core binary "01" (remember this is the rightmost digits of the binary), the work of the second task is moved onto the next real core.

Easiest way to avoid problems in P3D/FSX is to disable HT, then we are guaranteed that each task of the simulator is working only one per core.

With HT enabled the task count is doubled in the simulator because the simulator makes a task on each LP allocated in the AM. The AM is telling the jobscheduler that we want tasks allocated on certain LPs and the simulator tasks remain on those LPs allocated.

Most of the extra tasks with high LP counts (HT enabled or disabled) are pulling in data (e.g. scenery). As the task count increases, each time data is requested (we move into a new area in the sim demanding more scenery) there will be a hit on the CPU. With more tasks that's a bigger hit across the CPU but the scenery is pulled in faster. So we might want to limit the task count by using the AM HT enabled or disabled.

Using HT is a bit of a fiddle to get the best out of it for not much gain, at least not much in terms of FPS but reading in scenery is accelerated.

Also when HT is enabled and we use binary "01" (one LP) for each core, that leaves other processes outside the simulator to use those unused LPs of each core. If we get a high use process sharing the main task that brings down the FPS or even causes pausing. That's why we also arrange to have other processes (that run alongside the simulator) moved away from the cores of the primary tasks and so they only share with later cores pulling in the scenery, or spare cores. Generally we don't see many tasks other than the simulator tasks, but with addon exe processes the jobscheduler will be assigning them LPs with low use.

We can look into use of Fiber Frame Time Fraction (FFTF). With small FFTF values the time spent pulling in scenery is reduced to allow for higher frames per second (FPS).

Edited January 11, 20215 yr by SteveW

Can anyone suggest me settings for 8700K @4.8?

hi, you can try this one:

https://www.gfsg.co.uk/affinitymask.aspx?SubMenuItem=utilties

I have gone round in circles over the years, reading so many opposing opinions about this subject, to the point where in the end I gave up and simply did regular comparison tests and decided to run with whatever I felt worked for me, rather than try and run my PC as others say.  I have been running every version of P3D up to V4.5 with Hyperthreading off, with no reference to AF in the Cfg, each time with three iterations of I7 processors and have always had smoother flying. I can say this with 150% certainty.

Edited July 10, 20214 yr by Rockliffe

Around and around goes and comes this topic. I still bet that the correct AF setting makes turning off HT in the BIOS obsolete, with the advantage that you do not have to frickle around in the BIOS for applications that profit from HT. Then, if you buy your rig exclusively for P3D, I wonder why people choose an i7 just to turn HT off then...

@Druce I use an AF of 1365 for my [email protected] and this works like a charm. 

My professionally built PC by Chillblast (UK) specifically for flight sim came with HT enabled and they recommended leaving it on when I asked about it.

They know far more than me so I’ve stayed with it and with an AM of 1365 P3Dv4 and now v5 works great combined with a monitor refresh rate of 30Hz and VSync enabled.

1 hour ago, Ray Proudfoot said:

My professionally built PC by Chillblast (UK) specifically for flight sim came with HT enabled and they recommended leaving it on when I asked about it.

They know far more than me so I’ve stayed with it and with an AM of 1365 P3Dv4 and now v5 works great combined with a monitor refresh rate of 30Hz and VSync enabled.

Hi Ray, would you mind posting your CPU? Thx

24 minutes ago, SergioN said:

Hi Ray, would you mind posting your CPU? Thx

It's in his signature.

46 minutes ago, arwasairl said:

It's in his signature.

Thanks but still can't find it.

Just now, SergioN said:

Thanks but still can't find it.

It's in red. Intel i7-8086K o/c to 4.6Ghz

Just now, arwasairl said:

It's in red. Intel i7-8086K o/c to 4.6Ghz

Thank you !

On 4/19/2020 at 3:43 PM, Ianrivaldosmith said:

@Sethos I have an 9900KS. So 8 cores and HT on makes it 16. 
I added an affinity mask to disable the HT part of the cores. It runs way way way smoother. I tested it for 24 hours using the same scenario. And the conclusion is, that the hyper threading causes stuttering, and the affinity mask to turn it off removes the stuttering. 

Are you able to provide that affinity mask? Would like to give it a try. Thanks

On 7/10/2021 at 10:04 PM, SergioN said:

Thank you !

Except it's o/c to 5.0 Ghz

I have HT OFF it allows me to run the CPU variable boost no limits without hitting the heat limit.

 

 

I tried a lot of different settings using the information in this forum and think that HT on is better for me. In theory HT on should allow more work to be done for any given processor speed but does create a little more heat and thereby limits the max clock speed. I have an i7 8700K o/c to about 4.4 GHz and use an affinity mask to keep the main P3D work off cores 0,1,11 and 12. I then use Process Lasso to restrict various apps to using those cores. The FSLabs seems to be very well optimised and with 30fps set in NVidia CP and unlimited set in P3D it seems very smooth. I currently have all cores sharing the work fairly evenly and almost no stutters or fps drops.