Re Gsync: when the Main Thread is the source....

[Noel 4,504]

I'm considering a new screen for the following reasons:

• Gsync Ultimate Certified
• VESA DisplayHDR™ 600
• 38" curved 3840x1600 DP 144hz  or HDMI 85HzDMI: 85 Hz)

My current screen is 3440x1440 60Hz, no Gsync, no HDR

My understanding of Gsync, roughly, is that it was designed to be used alongside Vsync, such that when you are unable to maintain the frame rate establish by Vsync, Gsync will fill in frames such that you can then avoid the stuttering that ensues in Vsync when you can't meet the target frame rate establishws by your vertical refresh (and hopefully w/ a divisor as well, as we have in-sim, or thru other syncing methods.  It's possible I'm misunderstanding how it works so correct me if YOU understand how it works.

My question is this:  if the reason you are unable to hit the target frame rate is main thread overload, versus GPU overload, does Gsync still perform this role?

I get the distinct sense here the HDR isn't worth changing the screen for.  The screen I'm looking at is of course larger, but this only means I will move the display a few more inches away so will not really give me anything more ultimately. It's the same pixel pitch/density so will perhaps look a little sharper since it's farther away.

[Republic3D 1,232]

Real G-Sync, like the monitor you're thinking about buying, will work all the way down to almost 0 FPS.
I'm not really sure if it's 0 or 10 or 15, but my G-Sync works fine even in low FPS areas. 

My understanding is that it works when it's main thread limited as well. At least that's how I perceive my own monitor. 

[cianpars 1,166]

I have a GSYNC monitor and run with a LOD of 300 at ultra settings.  Unlimited fps really has the fans on my GPU going great guns and I get CTDs from time to time.  Turning off GSYNC and limiting FPS to 30 with VSYNC keeps the GPU much cooler and MSFS is much more stable.  For some reason the FPS limiter in the Nvidia software does not allow me to limit my FPS at all with GSYNC on.

[shamrockflyer 647]

4 minutes ago, cianpars said:

 For some reason the FPS limiter in the Nvidia software does not allow me to limit my FPS at all with GSYNC on.

You could try limiting fps via Riva Tuner.

[AnkH 2,268]

42 minutes ago, Noel said:

...Gsync will fill in frames such that you can then avoid the stuttering that ensues in Vsync when you can't meet the target frame rate establishws by your vertical refresh (and hopefully w/ a divisor as well, as we have in-sim, or thru other syncing methods.  It's possible I'm misunderstanding how it works so correct me if YOU understand how it works.

Well, actually some two second googling would resolve this for you, no? Small hint: yes, you completely misunderstood how G-Sync is working...

Link: https://en.wikipedia.org/wiki/Nvidia_G-Sync

[neumanix 114]

Gsync and Vsync are different ways to sync the GPU and monitor to avoid screen tearing. Gsync doesn't add any frames to smooth things out.

With Vsync you force the GPU to only output frames at a fixed rate, for example 60fps (~ every 16 millisecond) regardless the actual workload.

This fixes tearing but introduces latency as it always waits the same amount of time between frames.

Gsync is dynamic and waits only however long the frame took to produce, waits for that amount of time, then proceeds with rendering and outputting the next frame immediately.

This also fixes tearing but minimizes latency.

You need to stay in the specified fps range for your particular monitor for Gsync to work. Mine for example is 30-144Hz (fps).

You only need to use frame limiter (or add Vsync) if you exceed the upper limit.

If a game runs at >200 fps, I limit my fps to 140 to stay in the Gsync range and avoid using Vsync. I could also not use a limiter and instead use gsync+vsync and the game would run

locked at 144, but I find using only gsync with a little "wiggle room" gives great results.

Also, none of these techiques fixes stutters caused by loading and other costly tasks that happen from time to time.

Edited November 7, 2022 by neumanix

[bobcat999 8,484]

Just a note.  Riva Tuner SS (v7.3.3) stopped limiting frames for me on my 3080Ti with recent drivers.  Basically it just didn't work with the newer Nvidia drivers - worked before.
I couldn't find a newer version than 7.3.3. online.

However, I downloaded MSi afterburner to see if I could limit frames through that, and it comes with a newer beta version of RTSS that works!  Cant remember the version number, but it works very well again.  I was adjusting it down from 60 fps one click at a time, and the frame rate display in MSFS dev mode matched exactly with it!

I was going for 45fps as it doesn't stress everything too much, and I have a freesync ultra monitor (a cheap Gsync ) that works well at that refresh rate.

However, after swapping my 12900K for a deal I got on a 13900KF, it has helped matters enough to hold 60fps just about everywhere I fly now.  Looks and feels great at 60Hz 4k!  I noticed my 12900 was just topping out on two threads occasional, causing stuttering at 60fps.  This is gone now with the 13900.  So I was CPU limited not GPU (about 80% GPU at 4k 60FPS).

I just picked up a Tobii eye tracker 5 as well, so it makes looking around super smooth at 60Hz.  The only differences are the 13900KF (all cores 5.8GHz, but under-volted by 0.02v), and turning DLSS down one to 'balanced' mode - it is a completely different experience now.  In balanced DLSS, the flat screens are just a teeny bit more blurred than quality, but with the Tobii I can lean in towards the flat screens now and see everything in perfect detail anyway.

Doing aerobatics in the PC-21 last night, at 60Hz 4k, and looking around with the Tobii, was the best flight sim experience I have ever had.  Made me feel sick for a bit afterwards though!  

[Noel 4,504]

1 hour ago, AnkH said:

Well, actually some two second googling would resolve this for you, no? Small hint: yes, you completely misunderstood how G-Sync is working...

Link: https://en.wikipedia.org/wiki/Nvidia_G-Sync

Of course I googled this Chris but the internet is a giant place and there are more than one articles about Gsync.  

https://blurbusters.com/gsync/gsync101-input-lag-tests-and-settings/14

This article suggests the best solution is indeed from using both Gsync and Vsync together but it's much more than that even.  Perhaps that's changed since this article was written--perhaps it's as simple as Gsync utilizing VRR to sync the monitor's refresh to the GPU and there is no issue w/ tearing.  But...

What I really would like to know is what happens to frametime in this scenario.  I have recently experienced a level of smooth animation heretofore never experienced and it is clearly associated with essentially zero frametime variance.   I've tested several other Vsync methods and none of them is quite this perfect.  I can see the difference it is like analogue animation just totally fluid.  I have no idea how Gsync does insofar as frametime variance goes so wonder how the subjective experience is.  Right off the bat it seems like it might be the antithesis of zero frametime variance.  I don't think I will know unless I try it for myself.  

 

 

 

 

Edited November 7, 2022 by Noel

[neumanix 114]

Of course smoothness is based on the ability to produce stable frametimes, which we are unfortunately not blessed with in flight sims.

There are always these longer frames that will cause stutter no matter what, but Gsync helps and has nothing itself to do with frametimes.

They are what they are and Gsync will keep everything tear-free as long as the frametimes stay within the forementioned interval.

In a racing sim a use, I get rock solid 120fps (locked) ALWAYS, and therefore a perfect display using Gsync only.

[Noel 4,504]

2 hours ago, neumanix said:

Also, none of these techiques fixes stutters caused by loading and other costly tasks that happen from time to time.  Of course smoothness is based on the ability to produce stable frametimes, which we are unfortunately not blessed with in flight sims.

Ah but we are, or so it seems.  Right now I am using a method that keeps frametime variance to essentially zero, and this equates bigtime to the perception of smoothest possible animation at whatever framerate you're lock into by vsync, which in my case is 30fps.  This was the last 26 miles into KSTL in the AS CRJ700 captured by CapFrameX.   I wonder what happens to frametime variance, or perhaps more aptly what happens to our perception of 'smoothness' which I maintain is different from 'freedom from stutters', using Gsync w/ or w/o other technologies, 

Edited November 7, 2022 by Noel

[Noel 4,504]

1 hour ago, bobcat999 said:

Just a note.  Riva Tuner SS (v7.3.3) stopped limiting frames for me on my 3080Ti with recent drivers. 

Works here Rob w/ the latest NV GRD.  I did get fooled though because I had NVCP set to Vsync:  OFF,  rather than Per 3rd Party Application or whatever it says.

[neumanix 114]

If you lock to 30fps, the experience will be the same using Vsync or Gsync because you've locked your update to ~33ms.

With Gsync you let the game update as fast as it can and sync accordingly, frame by frame, no unnecessary waiting.

Edited November 7, 2022 by neumanix

[Noel 4,504]

1 minute ago, neumanix said:

If you lock to 30fps, the experience will be the same using Vsync or Gsync because you've locked your update to ~33ms.

With Gsync you let the game update as fast as it can and sync accordingly, no unnecessary waiting.

What happens if I use Gsync, and either CPU or GPU can not output to the lock so perhaps can only do 27fps at that instant?  Does stuttering still happen?

[neumanix 114]

Well, if the gsync interval starts at 30, then at 27fps it won't be able to sync that frame and you'll get tearing. No more nor less stuttering.

That frame will take 1000/27 = ~37ms. If you had Vsync active it will lock at 15fps, that's the next "half way down", and the frame would take ~66ms = feels more laggy.

That's how Vsync does it if a frame takes longer than what you've set Vsync lock to. For example if you lock to 60fps and achieve only 55fps, then Vsync drops to 30fps.

Vsync locked at 30fps and achieving 27fps would sync at 15fps.

Edited November 7, 2022 by neumanix

[Poppingcork 24]

Great info!!