CPU Bug "Limited by Main Thread" is causing the bad FPS

SInce last update, suddenly performance go down. i used to fly over over trasantlantic flight, more than 8 hrs flying wihtout any performance lose, since new version release, every flight that have more than 2 hrs, suddendly frames fo to 10 fps without any reason over sea. and FPS counter show limited by mainthreat, any explanation or root cause? or way to fix it? now im limited to short flights. using last version over 747, 787 and a320. same issue

funny, considering i have a i7 7700k clocked @ 5.2 with 64GB DDR4 XMP 3200 and a 1080FE and at 1080p res, im getting 45-60 fps globally no matter what i do where i go.

you failed to mention what resolution you are using and any contributing factors such as TAA, 16x AF/AA Settings, DSR and any other performance hindering features within the NVidia Control panel.

Im using standard configuration in NVIDIA Control panel, only change is to maximum performance, inside MSFS 2020 im using ultra with about 40-60 everywhere. i have a gtx 2080 and I7 9750 32 gb ram and intel optane SSD with 1500 Mb/s
Suddenly drops from 60´s over the sea to 10 and no way to Go up after 1 hr later.

restarting the game, again i get 40-60s

CPU Usage averga from 30 to 60% in the worst case.
GPU Usage average 60 - 99% in the worst case

not sure why it did not tag the OP, since i was replying to him, but, i guess in your case, no issues for me.

the only time i even have the slightest issues, is if i use Sim Rate adjustments and when scenery gets loaded in as i move about.

Pretty much the same. Am running a RTX 2070 and a Ryzen 5, but whatever settings I use I basically max out between 30-35 fps whether it’s low or ultra settings. All cores are operating on even basis at 16% so personally I’m not sure what’s holding back better performance.

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@anon33898240 @SyBeckUK Sounds like you guys are relatively new to this thread and maybe haven’t read the whole thing - apologies if I’m wrong. But throughout this thread, a number of us have been probing at why the game struggles etc and have largely come to the conclusion that it’s being limited by single core performance on the CPU on most systems. This is because the game engine is not yet well optimised and there is no DX12 support to help offload task to the GPU.

@anon33898240, it’s interesting what you say about having no issues - although not immediately helpful to everyone (essentially translates to “no issue for me so must be no issue”) - since I have the same CPU and an RTX2070 Super. The difference is that mine is not overclocked. The reason I say this is interesting is that given what I’ve said about it being largely limited by single core CPU performance, I expect my performance to improve with an overclock - which I’m going to try today.

Using the dev tools, a number of us in this thread have seen that the game is being “limited by main thread”. This is the same in my case in most situations, with the game only becoming GPU bound when I’m at high altitudes/low scenery areas, in stable flight where I’m getting very good FPS anyway. In other words, my GPU can only push around 70FPS max beyond which it doesn’t stand a chance. The CPU range on the other hand can go higher than 70FPS but most of the time is the limiting factor, especially when things get “busy”.

This is why I’m going to do some experimenting with some OCs and see if it helps. My intent is to see if I can make the game GPU bound more of the time. Currently, it’s almost always CPU bound when I’m on the ground or close to it. The closer I can get to the ground while still being GPU bound, the more successful I’ve been.

Guys i have a Samsung 144hz 3840/1080 3900x + 2080 super +64gb of 3600 ram corsair all stock all ultra settings then custom and i was having same issue what i did was start it playing with the settings while flying over Disney World on a da62 wich is a fps eater and now went from red to pink and it says gpu limited wich is what supposed to say no more cpu thread limited also not every time lower settings are best and dont go by fps go by smothness…thats until i buy the 3090 :slight_smile:

@Rrryan300 - this sort of misses the point. Sure you’ve got it to be GPU bound but you’ve done so by reducing what the CPU has to load in. I think I speak for everyone when I say that we know that reducing the settings will give better FPS. What we’re saying is that Ultra should be supported on the best hardware you can buy right now and it’s not - at least not with steady frame rates. This is down to the CPU optimisation issues we’ve been taking about for a few weeks now. We’re therefore looking for ways to alleviate this without having to turn all the detail down.

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In all previous flight simulator releases, the “max” settings were always for hardware you can buy in the next 2 years at least, not for today’s hardware. It might be the same here.


cool ok i htought this was about the cpu main thread message,by the way my fps stay same as if it was on ultra

So I’ve done some experimenting and I did seem to get a slightly better FPS after my overclock.

Before, my CPU was running around 4.6GHz in-game, and flying into Barcelona I was getting about 25 FPS at the worst.

Even though I seem to have lost the silicon lottery (max overclock I could get stable was 5GHz on all cores), after the overclock I was getting about 30-35FPS at worst.

Still showing it being bound by main thread on approach but evidently better performance. Seems to support what’s now become the running understanding that this is CPU bound by a single core (1 of my cores was always at 100%).

Therefore, my conclusions on this are that:
a) you can get better FPS out of this game by overclocking your CPU
b) adding more cores does not help. this is down to the way that the game uses CPU cores
c) DX12 should help (when it arrives) since it’ll help offload the CPU
d) the main improvements (beyond extreme overclocking) to the frame rates of this game are going to come from optimisations of the game engine

On the final point, having spent about 100hrs in the sim at this point, I can’t help but feel this is why they have not yet given a release date on xbox. Sure Xbox Series X is going to be “next gen” but it’s not going to be more powerful on a single core than most of the PCs people are using in this forum topic. Therefore, I think they know that the single core performance is holding it back and that to release it on xbox in the current state would make a lot of console gamers (who are more likely, even than some on these forums, to expect the game to run flawlessly out of the box) very very upset.

This therefore gives me hope that they are actively working on it and that failure is not an option for them given that they have committed to releasing it on xbox.

I’d be interested to know whether any of you are able to do a back-to-back FPS comparison between CPU at stock speeds and CPU overclocked. Seems to be the way to go, even if my chip does seem to be one of the lowly binned ones.

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Agree with your assessment about the XBox. They have their work cut out for them to get what now requires pretty powerful pc specs.
On the OC when I was running an i5 6600k I was able to boost it from 3.6 - 5.1 and did see a nice fps bump.

im hardly new, had you done any bit of checking, ive been part of these forums since Dec 11th and the first iteration of the Alpha Testing. YOU on the other hand with a Join Date of August 23rd are new to the forums.

ive handed down more help than you can imagine.

the game is NOT bound to single CPU threads, Myself and countless others have proven it via means other than the internal dev mode checker.

the game is poorly optimized yes, i will agree on that. that being said, many of us in areas of the forum you cannot see and i cannot re-publish that data without re-writing the entire post have solved the mystery of thread performance.

now, what i will give you in terms of alleviating some of the optimization woes, are you running Windows version 2004 ? and have the latest nVidia Drivers?

if not having BOTH of those, you will not get DX12 support anyways, since its a requisite of DX12 to have Windows Build 2004.

Windows 2004 brings about a new feature also known as Hardware Accelerated GPU Scheduling ( refer to this as HAGS from here on )

Before i updated to Windows 2004, i had lots of problems with stuttering and poor performance in low altitude heavy density scenery areas, once HAGS got put in place, all but the minor amounts of stuttering occur only during Scenery loading.

Another thing is, using the nVidia Control panel to force certain settings helps get better performance than leaving everything on automatic and app controlled.

since i override many of the settings the sim provides and use a blended set of settings within the sim, but override more in depth ones with the NV CPL, that is why i get no issues.

Game resolution is also a key factor, which no one other than myself and 2 others have posted what resolutions they are running at. Since im running 1080, on a 1080 Founders Edition, and have no problems, maybe, just maybe, its user error and user inability to provide key information that could help others point out tips and hints that will fix these problems.

A lot of users that complain of low FPS, fail to mention they are operating at 4k and 1440p resolutions, trying to use RTX and other very heavy GPU intensive settings that hinder raw FPS Performance and then wonder why the sim is lacking. when its clearly USER FAULT.

so maybe you should do a bit more research before blasting someone not knowing a thing about them with simple profile checking.

good day sir

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Pour ma part je pense que vous êtes dans le vrai concernant la (v) ram.
Perso j’ai un 9900K et 2080 super (8G vram) et 32G ram et je rencontre des problèmes de fps, la 2080 super est saturée à 99% de charge.

@anon33898240, woah buddy. No need to come in so hot and aggressive.

Firstly, if you re-read my response, I said that it was possible that you guys were new to the thread not the forum. I noted that you had been around since the alpha and wasn’t trying to insinuate anything else. Merely that your response didn’t seem in-keeping with the flow of this thread and perhaps you were new to this particular topic.

Secondly, you say it’s not bound by single core CPU performance and that you have “solved the mystery” but you don’t clearly state what you determined to be the root cause. As far as the data we’ve collected on here, along with the experiments we’ve done has led us to the conclusion that it is single core CPU performance. This is also backed up by the immediate increase in performance I got when I overclocked my CPU - see my next post after I’d replied to your post. I appreciate that you don’t want to repost a whole thread here but maybe you could provide a link to help us see the light?

You ask whether I’m running latest version of windows and drivers. The answer is yes, I am. However, you also seem to infer that doing so will somehow unlock DX12. This is untrue. This game runs on DX11 and has nothing to do with versions of windows or drivers. DX12 support could only be added through a patch (i.e. through game code) not through having the right mix of versions of unrelated software.

You also talk about HAGS, I’m running that. I am also overriding a number of settings from NVCP.

You mentioned that I haven’t said what res I’m running at. You might be right, I can’t remember whether I’ve said it previously in this thread but I’m running at 1080 since that’s as high as my display will go.

However, you also seem to be operating under the incorrect impression that this is an RTX-ON game. It’s not. Simply having an RTX card does not make every game ray-traced. I’m running an RTX 2070 Super Founders Edition which when you compare CUDA cores (where the calculation is actually being done for this game) it’s the exact same number as the 1080, along with pretty much the same base clock speed and a higher boost clock speed. So your inference that either my graphics card is slower than yours or that I’m weighing it down with overly heavy modern graphics options that you can’t turn on is simply incorrect.

So with everything above, I offer the following:

  1. My apologies if you felt like I was attacking you. I had not meant it that way. Although I will point out that your response was pretty aggressive.
  2. You tell me to do some research when, as you can see from my response above, it seems that it is you who is under-informed about how computing and graphics technology works.
  3. I refute your suggestion that the issues that I and many others are suffering from are “USER FAULT”.
  4. But I also offer the olive branch for you to provide a link to the thread where you guys have previously “solved the mystery”. I’d love to read it since we’re all trying to get to the same point of having a buttery smooth gaming experience.

Looking forward to reading your response.

Have a good one.


Non, je ne pense pas! Si vous utilise la “developer tools”, on peut voir que la (v) ram et la ram de la systeme n’est pas utilise 100%. Je ne sais pas si on a lu la thread enitre, mais nous avons trouve que c’est une probleme de comment la programme vont utilise la CPU.

Il y a un hyperlink a le site “Toms Hardware” ou ils trouve que apres un i5, il n’y a pas beaucoup de difference de FPS parceque c’est un issue avec la performance de la CPU avec une core seulement. Le i9 a plus des cores que le i5 et i7, mais les cores sont pres-que aussi vite que les autres, donc il n’y a rien de amelioration.

P.s. Je suis desole si ma Francais est horrible a lire, je suis Anglais et je ne sais pas la methode a inserer les accents!

you are not a Alpha tester, i cannot provide you that link its a closed section you would not even get a valid response even if i did, and i would be facing disciplinary actions for doing so. so sadly, i cannot share the info via a link since its Alpha Program content and still NDA Bound.

im a 18 year IT Specialist with hardware, networking and security focuses and as a person with a CS Master’s Degree, CISSP, CCNA and MCSA Associates Degrees and 16 trade certifications from CompTIA and Microsoft, i assure you i know a exponential plethora more about this field than you think i do.


I did not say RTX is mandatory on, i said many people enable it which is a extreme burden to even the 2080 Ti and then simply think, oh, i have a 20 series card, i can turn everything on and then come here to complain about craptacular performance, that is USER FAULT.

Im not new to this topic either, ive read it since the day it was posted. im online and in these forums almost every day. i tend to avoid most of the topics that are petty or otherwise contradictory to the progress of making this sim even better than its day 1 release. you took my reply into its own context because myself and many other testers figured out better performance by tweaking at least 8-15 various aspects of video settings, in-game, within graphics control panels and windows.

im not going to spend 2 hours rewriting the entire topic that was discussed, even generalizing that topic from the alpha section would take me an hour minimum to collaborate the data and create the necessary images and guides to go through all the settings as suggestions.

native DX12 code was added to 2004 and pending games supporting it will have to be done by each developer, games using or claiming DX12 support are not NATIVE versions. you assumed that stance, and thus are twisting what my comment referred to. Windows 2004 is a prerequisite to even touch Native Dx12 support. good, you have it, so do i. in fact im running Windows 20H2 and im seeing even more improvements on multiple games FPS Wise.

also, if the game is relying on single thread performance, why is everyone’s task manager and other monitoring software reporting usages on EVERY core and thread when the sim is running? my MSi Afterburner has a dedicated monitor for it, and i see all 4 cores and 8 threads showing activity from FS 2020, so obviously its tasking more than one thread on the CPU. Asobo could have EASILY labeled the MAIN Thread as overall CPU tasking, ive seen that before in other alpha projects.

implying that the sim is only using a single core/thread is outright incorrect. if that was true, then only a single core/thread would be getting utilization, let alone a single core ( when hyper threading is present, can lead to a HT Thread being used over a physical core ) is going to maxxed out and the others left at idle states. We have already seen lots of confusing information since Asobo is a French Company and English is not their native language.

your optimizations and understandings are far different from mine, might i suggest you play around with other things than just clock speeds.

Power Profiles, CPU Tasking and Park Controls among a bunch of other things in the NV CPL.

CPU clock speeds is just one of at least 30 things you can adjust.

the fact im using older hardware and getting better performance than newer hardware indicates i know how to optimize my system better than most.

and im not going to debate or otherwise go back and forth with you on this subject any more.

it took me 6 days of tweaking multiple aspects of settings to get the sim where i have it now, and since EVERYONE has different hardware and profile settings, there are infinite number of suggestions and settings to use that could give you the same results. YOU, and only YOU, can take the time and make the effort to test them out on YOUR hardware.

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But that’s exactly the issue then, do we need PhD in computers to setup the game to run properly.

Would the likes of Nvidia and Microsoft be able to adjust the profiles based on hardware capability to get reasonable performance and/or optimise the game?

I can see that Nvidia has drivers and profiles for the game.

It seems that I don’t have to do it, or at least I am happy with, playing other games.


since FS 2020 is so new, it takes time for the profiles to be tested and verified before they get published to GF Experience.

quite honestly, your own testing is far better.

Im reading your wall of text, but i just have to point out that being CISSP, CCNA means jack ■■■■ when it comes to troubleshooting desktop hardware and performance.

MCSA degrees (IM MCSE in multiple fields myself) are easy to get and nothing to really brag about, and i find they only teach you what Microsoft wants you to know… ie. useful in theory, useless in day to day use. You will start seeing that when you get some experience under your belt.

If a game/sim like this is causing widespread performance and stutter issues… the developpers really didn’t do their jobs right or failed to fix the underlying issues causing this. Unless the goal is to create a game/sim that is very fickle and stuttering is a feature… ofcourse.

As others have pointed out, if you bring a sim or game to the market it shouldn’t be exclusive to people who are proficient on the level you claim to be. Don’t make excuses for the developpers.

And to top it all off, you know what fixed my stutters? Prioritizing background processes over MSFS… first game i ever had to do that with - and my CPU, Memory and GPU still have headroom spare.