And when you enable DEV mode it doesn’t need this small flight log connection, which makes it smooth. Right? I remember that people complained that the first beta of SU8 had some problem with saving flight and that’s where it all started, in the second build of the beta SU8 already presented the stutter in a more notorious and severe way. The problem may actually be there, they messed with the way the flight log (small logs) is executed and for some users like me who are from STEAM this causes problems… so let’s move on!
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Correct about Dev Mode. Flights are not logged when it is turned on.
So better having hags on or off?
I tried both. HAGS off still seems to be the way to go.
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Can’t say I’ve noticed a difference either way. I usually have it on, assuming it might be squeezing out a tiny bit extra performance (after all, that’s what Microsoft says it’s for right? 
I often adjust the TLOD depending on where I am flying. I can easily fly with 400 TLOD in some mountainous areas, or at high altitude, but not at low altitude in dense photogrammetry areas (with CPU boost disabled).
I made a wishlist item asking Asobo to decouple photogrammetry LOD from terrain LOD, but I don’t see that happening due to the way the game is designed.
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my main thread is only seeing 30-40% useage (12900k) and my GPU at 60% usage and yet I still get huge stutters even with frames locked at 30fps
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You are likely main thread limited in Dev Mode.
what does that mean?
You can open the FPS counter in Developer’s Mode in your settings and see what is causing the slow down. Odds are it is the Main Thread.
What is your processor and what is your Terrain Level of Detail set to?
Do you mean Core 0 Thread 0 usage is only 30-40%? No other cores with higher usage? I’m not even certain the mainthread runs on C0 T0. I was just making that assumption.
ah yeah main thread limited - but why is it limited by main thread when it’s only working at 40%?
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yes core 0 - all other cores are generally lower. core 10 spikes sometimes but the max on any core is 93%. I tried turning off the E-Cores on the 12900k to see if that helps plus turned off hyperthreading to see if that had any effect but neither make a difference to the stutters
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This is the $64,000 question!
Especially when no CPU is running at 100%.
Main Thread cycles can run quite slowly in busy, scenery dense areas even when a computer looks to have the overhead to handle things.
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Go ahead and turn hyper threading back on. This slowing doesn’t seem to pertain to one core hitting 100% and slowing things down… not in SU9.
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agreed and HT is already back on 
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The main thread might be getting stalled waiting on other threads and/or returns from system calls. Process Hacker can show the amount of system calls and possibly even drill down to IO and other things.
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That would be interesting!
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Here’s the latest nightly build Downloads - Process Hacker
You can find “System calls delta” under System Information > CPU tab (at the bottom)
See if there’s more system calls at mainThread limited areas versus other areas for example.
Edit - The system calls/sec performance counter is also built-in to Windows and you can access it (along with many other counters) in MSI Afterburner, and add it to your on-screen display.
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It’s amazing how many people simply don’t understand how the vast majority of games interact with their flashy new CPU. This is my understanding of how things are at the moment.
Ordinarily, according to RivaTuner, my CPU (a 5900x) is 11% utilised. What you have to understand is that that means only 11% of my 12 core / 24 thread CPU is being used to run the game. Because of the way the game is coded all the CPU demand is being put through 1 or 2 cores, the rest is effectively sat doing nothing. So although only 11% of the total capability of your CPU is being used, the 11% that is being used is maxed out. You could have a 60 core CPU (if it existed) and it would make no difference to the game right now.
Flight Sim is not unique as almost every game out there suffers from this affliction. Unfortunately, where CPU manufacturers are charging ahead making CPUs with ever more cores and threads, software creators are not on the same train. My simplistic view is that they’re still designing software based on the way it was done a decade ago because they’re often under pressure to churn out games to make money. It’s not a criticism in any way to say that it’s easier to take the line of least resistance when faced with that pressure.
In theory DX12 allows the spreading of CPU load more across the whole CPU, but game designers have to code their games to take advantage of it. Given huge chunks of FS2020 is code simply lifted from FSX that is not an easy thing to do. Asobo are doing it, slowly but surely, but it’s not going to happen overnight.
This is why what @WellREDBarron has been saying is so important. Turning your TerrainLOD up to the max, experiencing poor performance but noting that your CPU is only 10% utilised is the root cause of many peoples problems. Match the CPU load of the game to the capability of your Main Thread and you’ll have a MUCH happier experience all round.
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