Sign in to follow this  
Brian_A_Neuman

Question about Tweaks

Recommended Posts

Good Morning (Or afternoon depending on where you are in the world),

Recently I made the switch from 3.2 to 3.3.5 and did a full clean install of everything (Planes, Scenery you name it) to include a full and clean install of the actual program when I made the change to Windows 10.

Now, I was using a copy of the previous Prepar3d.cfg file that had tweaks such as the fiber frame time fraction: .01 and the Affinity Mask set to 14. 

I read somewhere, and I cant remember where, that these tweaks are no longer needed and provide no real benefit in P3D. Can anyone confirm or Deny it? I just had P3D rebuild a new .cfg file to address some performance issues with the Aerosoft Airbus series, but I need to know if these lines should be added again. Thanks in advance for your help.

Share this post


Link to post
Help AVSIM continue to serve you!
Please donate today!

Good Morning (Or afternoon depending on where you are in the world),[/size]Recently I made the switch from 3.2 to 3.3.5 ...I read somewhere, and I cant remember where, that these tweaks are no longer needed and provide no real benefit in P3D. Can anyone confirm or Deny it? I just had P3D rebuild a new .cfg file to address some performance issues with the Aerosoft Airbus series, but I need to know if these lines should be added again. Thanks in advance for your help.[/size]

Yeah... I'm replying here just so I can see you the answer to your post.

 

Cheers to all especially those who respond,

 

Chas

Share this post


Link to post

Affinity Mask and FIBER_FRAME_TIME_FRACTION still work as intended when added to the prepar3d.cfg. But, if it is still needed or not is depending on your setup and the other tweaks you are using. In my case, FFTF results in a warping-like appearance of P3D, I eliminated this one out of my config (the value 0.01 is anyway bull***, as it reverts to the next acceptable level, which is 0.10). The Affinity Mask entry I still use because I do not want to turn off HT but my P3D seems to run smoother with AF added (I have a i7 3770K and use the AF value "85"). Besides that, the only "tweaks" I currently use in my config are an increased value of TEXTURE_BANDWITH_MULT, I currently use "1800" there, and "UseGlobalTerrainView=true". That's it. And I never had a better simming experience than now.

Share this post


Link to post

Affinity Mask (AM) decimal 14 = binary 1110, ones represent "On" logical processors (LPs) and zeros represent off LPs. The first LP in the binary representation is on the right. In the case of AM=14=1110 then, the right-most LP is zero. This means that the app would utilise just three LPs. If Hyperthreading (HT) is enabled then there are two LPs per core, and so only two cores would be used, one LP of the first core (core 0) and two LPs of the second core (core 1). With Hyperthreading disabled, three cores would be used, LP 0 (core zero) would be ignored and LPs 1,2,3 (cores 1,2,3) would be utilised.

 

Depending on the app, here talking about P3D, there is another requirement, how does P3D work with respect to HT and core Affinity. Well, P3D counts the number of LPs, those ones in the AM are unmasked LPs, and makes special fixed threads on all of these LPs. Put very simply the first thread job is the renderer, and when there are four LPs made available, the renderer is at it's leanest. If there are less than four LPs, the renderer job does work that would otherwise be done in other jobs. If there are more than four jobs the arbitration of those extra jobs is more work in return for faster scenario loading, and a slight overhead on the rendering job. In the case of P3D v3.2+ the overhead on the rendering job is very small with more than four jobs. The next two jobs after the renderer organise loading scenery, the fourth job loads scenery. The fifth to N jobs also load scenery.

 

If we have an eight core CPU with HT enabled P3D will make 16 jobs if no AM is presented. The first core will run Job one and Job two, the second core will run jobs three and four, the remaining six cores will run 12 scenery loading jobs. This is quite probably not the desired outcome, since we would want to have the rendering job to itself, and, especially with many cores, 16 or more jobs may be too much and overload the renderer and thread arbitration jobs. This is why many turn off HT so that only 8 LPs are represented, the problem is only halved not solved, and each simulator job gets a whole core to itself.

 

Instead we can enable HT and turn off alternate LPs with the AM. So for example with a four core HT disabled No AM=1111, this is a good setup for the sim, but when we enable HT and we have No AM=11,11,11,11 (I put commas to separate the cores). This obviously puts the first four jobs onto the first two cores and is not desirable, again leading to folk turning off HT where the situation is not fully understood. In this case we could turn on HT and use an AM=85=01,01,01,01 where it can be seen we get one job per core, and yet still benefit the system overall with HT enabled.

 

More importantly it is where addon exe apps place their jobs that scupper the sim performance, not the AM or CPU used. It is better to start the addon exe apps above the rendering thread job of the sim, since none of the other sim jobs need to be so punctual as the renderer job and can take their time sharing cores with other processes running alongside the sim.

 

Remember that without an AM, HT enabled cores will do twice as many threads and can get hot, even too hot when loading scenery. However, even when one LP of each HT core is masked, perhaps with the example 85, the CPU will make more heat with HT enabled because it does more work.

 

 

The FFTF setting depends on the scenery and works best in the range 0.1 to 0.4 depending on the scene and the sim configuration, and so the default value is set around 0.3 without the setting in the cfg.

Share this post


Link to post

Steve, how many times have we been through this? :smile: you have stamina!

Share this post


Link to post

Yeah, even so, for each there will be at least two more posing the question. hehe

Share this post


Link to post

Well, you will get various answers to your questions but I myself stopped using performance tweaks the day P3D v2 had been released. If you used them in 3.2 and they served you well there you might keep on using them in 3.3.5 (afaik the step from 3.2 to 3.3.5 didn't make certain tweaks ineffective or redundant or whatever) but the question is: did they really serve you well or did you simply use them because you found those tweaks on the internet and decided to use them without actually testing them? Anyway, I always advice everyone to stop tweaking and keep the cfg as vanilla as possible. Back in the FSX days the consensus was you needed tweaks (and I tweaked the hell out of FSX) but I think with P3D the concensus is to first give things a try without tweaking.

Share this post


Link to post

The best tweak for P3D is to delete the Prepar3D.cfg file and let Prepar3D rebuild a fresh one. Then tweak your sliders appropriately.

Share this post


Link to post

We must be careful when referring to Tweaks. There are tweaks and there are system settings. FFTF is a tweak and AM is a system setting. The adjustment of the AM is system dependent but won't net any major increases in fps over no AMs. A four core i5 with no HT is a great performer with no AM since the sim gets four straight cores with no hyperthreading complications. Using AM=14 on that CPU would compact the sim onto three cores, and leave one free of the sim, the jobscheduler will likely start all other exe's on that and the sim will continue to perform well. AM=14 is shown in the P3D guide as a reference to this and is not a recommendation of the AM to actually use.

 

So to conclude, in the No AM case we usually always get good performance, but it's just not optimised. Getting it right can net 3-5%, could be worth it to some.

Share this post


Link to post

The only one I still use is the AM=14.

 

I have an "old" i5 2500 ( no HT ), and it provides me with better results.  Active Sky installers also prompt for the implementation of this "tweak", and since I use them it is done automatically whenever I install their products.

 

Other than this, I have all autogen OFF, mesh resolution une step bellow full right, no AI traffic or car / boats traffic.

Share this post


Link to post

Yes that's right, they do that because addon processes will be started on LP zero since there's less happening there when an AM like 14 is used (misses off the first LP). A quick look at the other three LPs will show all active, especially when loading scenery. Problems come when HT is enabled and then the addon scuppers the sim performance - again resulting in HT recommended off, even though it's not the right answer.

 

With HT enabled the proper recommendation for leaving the first core free on the four core would be 116. This leaves the entire core zero free (LPs 0 and 1). And also breaks the sim into four pieces, with the first job having a core to itself, and the only ganged up jobs on the third core never max out together, so in a way have the core to itself. Therefor AM=14 with HT enabled is a mistake.

Share this post


Link to post

Thx Steve, and yes, the AS16 recommended AM setting depends on the CPU in use - it's 14 in my case because I'm on a 2500 ( no HT )...

Share this post


Link to post

Thnx José. Yes a pretty good CPU in it's day and still works well today.

Share this post


Link to post

The best tweak for P3D is to delete the Prepar3D.cfg file and let Prepar3D rebuild a fresh one. Then tweak your sliders appropriately.

I second that. Luckily FSX tweaking times are over... In P3D it may more harm than help.

Share this post


Link to post

In the same way that I've stopped chasing fantasy FPS numbers, I have also stopped tweaking. With a relatively modern PC and more efficient and optimized versions of P3D I'm not entirely sure what you would reasonably expect to achieve.

 

There are very few people on these forums who know what they are talking about when it comes to tweaking. Most of us are just hacks. Flightsimming is far more enjoyable if you forget about tweaking.

Share this post


Link to post

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this