MSFS forums claiming 64GB of Ram helps on 3090s

[fogboundturtle 2,708]

I am flying towards KSFO and my VRAM using is 8.7GB on a RTX 2080Ti. 

[Ianrivaldosmith 5,317]

7 minutes ago, fogboundturtle said:

I am flying towards KSFO and my VRAM using is 8.7GB on a RTX 2080Ti. 

With VR or without? You will probably use way less outside of VR. 

[fogboundturtle 2,708]

I am not using VR. I am on Ultrawide resolution. on high end settings.

[Ianrivaldosmith 5,317]

8 minutes ago, fogboundturtle said:

I am not using VR. I am on Ultrawide resolution. on high end settings.

Doesn't use nearly as much as in VR. VR uses loads, sometimes you're pushing between 15-20 million pixels. I too have an ultrawide, 3840x1600, and even with render scale at 110 (Which looks magnificent btw) it is still only 7.5 million pixels 

[fogboundturtle 2,708]

1 minute ago, Ianrivaldosmith said:

Doesn't use nearly as much as in VR. VR uses loads, sometimes you're pushing between 15-20 million pixels. I too have an ultrawide, 3840x1600, and even with render scale at 110 (Which looks magnificent btw) it is still only 7.5 million pixels 

oh I know I have a Pimax 5K+ HMD. 1440p on each eyes. It would just kill my PC trying to run at the resolution so I just haven't tried.

[RXP 2,338]

22 hours ago, RXP said:

On my 2070S test system I've never exceeded VRAM resources except over the WU3 London, and this shows immediately with several GPU monitoring tools the game is oversubscribing the available VRAM and FS2020 is trying to purge older buffers to make room. During this time the CPU/GPU sync causes the render loop to stall until recovering and until the next few moments afterward it is oversubscribing again.

In case this helps understanding what I was referring to in the comment above, I've commented more about this specific problem a few days ago:

https://forums.flightsimulator.com/t/solution-for-stutters-pauses/198328/446?u=cptlucky8

 

Otherwise, about using 64GB with a 3090, there are positive feedback (at least 1 :-) )

https://forums.flightsimulator.com/t/solution-for-stutters-pauses/198328/458?u=cptlucky8

[Ianrivaldosmith 5,317]

So, sitting at Dublin airport, I was using 9GB VRAM using 2D. Switched to VR and it immediately jumped up to 13.5 GB VRAM in use.......... RAM was around 20 GB in use, and apparently 16GB was reserved ..... 

[EmaRacing 302]

4 hours ago, Ianrivaldosmith said:

here is me literally just now, in innsbruck in VR 

 

That's allocated memory, there are not 12Gb of textures loaded.

[Ianrivaldosmith 5,317]

6 minutes ago, EmaRacing said:

That's allocated memory, there are not 12Gb of textures loaded.

So. Why does it drop the moment I exit VR? 
And, what happens if you don’t have the memory to allocate? 

[RXP 2,338]

51 minutes ago, EmaRacing said:

That's allocated memory, there are not 12Gb of textures loaded.

Are you sure about this?

I've been trying to find more details about Task Manager and the only pertinent information I've found is:

https://www.extremetech.com/computing/251763-microsoft-shares-new-details-gpu-monitoring-capabilities-windows-10-fall-creators-update

Quote

First, last week, we questioned whether the GPU would report total memory requested (which is what tools like GPU-Z do) or actually report total memory utilized. Here’s what Microsoft had to say:

The memory information displayed comes directly from the GPU video memory manager (VidMm) and represents the amount of memory currently in use (not the amount requested). Because these are exposed from VidMm this information is accurate for any application using graphics memory, including DX9, 11, 12, OpenGL, CUDA, etc apps.

Under the performance tab you’ll find both dedicated memory usage as well as shared memory usage.

Dedicated memory represents memory that is exclusively reserved for use by the GPU and is managed by VidMm. On discrete GPUs this is your VRAM. On integrated GPUs, this is the amount of system memory that is reserved for graphics. (Note that most integrated GPUs typically use shared memory because it is more efficient).

Shared memory represents system memory that can be used by the GPU. Shared memory can be used by the CPU when needed or as “video memory” for the GPU when needed.

If you look under the details tab, there is a breakdown of GPU memory by process. This number represents the total amount of memory used by that process. The sum of the memory used by all processes may be higher than the overall GPU memory because graphics memory can be shared across processes.

 

Edited March 1, 2021 by RXP

[EmaRacing 302]

6 minutes ago, Ianrivaldosmith said:

So. Why does it drop the moment I exit VR? 
And, what happens if you don’t have the memory to allocate? 

Because it's not allocated anymore.
If you don't have it, it doesn't allocate it.
There is not enough bandwidth for all that vram to be used in a game. the ones that can make use of it are graphic designers, architects, content creators and such. Basically someone who can't afford a Quadro, but needs something to chew through their work.

Don't misunderstand me, it's a beast of a card for gaming, but not because of the vram.

[blueshark747 1,843]

10 minutes ago, EmaRacing said:

Because it's not allocated anymore.
If you don't have it, it doesn't allocate it.
There is not enough bandwidth for all that vram to be used in a game. the ones that can make use of it are graphic designers, architects, content creators and such. Basically someone who can't afford a Quadro, but needs something to chew through their work.

Don't misunderstand me, it's a beast of a card for gaming, but not because of the vram.

Interesting!

[RXP 2,338]

1 hour ago, EmaRacing said:

Because it's not allocated anymore.
If you don't have it, it doesn't allocate it.

The Microsoft representative cited in the article is saying something else if I'm not mistaken:

- It reports memory "currently in use", which could be just memory allocated (CreateBuffer for example) even if the application is not using it yet. However Video drivers are smart enough to also delay such allocations until first use in order to reduce the pressure on VRam. Because of this there must be a closer relationship between "allocated" and "in use" at the same time, but this corollary is not guaranteed.

- VRAM usage varies with allocations/use. If the VRAM amount value is getting down, this means some of the allocated/used VRAM buffers are destroyed. Please note though a buffer could be discarded but not free yet (I won't enter details in this short post). In the case an application is discarding a lot of buffers at once and is creating new buffers right after, it is possible therefore the VRAM pressure is higher during a certain time, until the discarded buffer are freed.

- When over allocating the VRAM amount, the driver may allocate buffers from the system memory instead. When the video card need to access the buffer content though, it might stream the content from RAM to VRAM so that the shaders can do their work on the buffer bits. In this case, it will stall the rendering loop during the time of the transfer.

 

With all the above said, a DX11 driver having up to 24GB VRAM available can be less agressive in the discard/free process and maintain buffers longer in VRAM memory when there is ample room, which could explain why in VR (and maybe just because of the way FS2020 is using the DX11 API when in VR), the application is allocating/using more VRAM than in 3D. However if this is the case and all of a sudden FS2020 is creating lots of other buffers, the driver will have to free a lot of longer-lasted buffers all at once and cause more stutters/stalling from time to time, whereas should it had freed these buffers regularly instead, the stalls would have been shorter and spread out over time (maybe so much to be a non-issue in practice). In any case, the driver is reserving up to 16GB system RAM in case it needs it, and it is possible these are not just reserved but also used RAM when VRAM fills up with buffers which should have been discarded sooner but weren't, due to DX11 maintaining buffers longer in VRAM when discarded but not freed yet.

Of course this is just speculation, albeit from technical understanding of how video card drivers are working internally in terms of resource management, but there are a lot of assumptions as well. In practice though, there are a number of people with a 3090 reporting much shorter load times and smoother flights with 64GB RAM instead of 32GB RAM, and this can only be attributed to me to having more RAM to accommodate the RAM needs of the simulator, the same RAM being otherwise amputated by some amount because of the 24GB and the DX11 driver.

For those wondering about the XP11 6 months Vulkan beta, most of this time was about fine tuning the memory manager, this might give you a small glimpse of why this is a complex matter.

Edited March 1, 2021 by RXP

[Glenn Fitzpatrick 3,798]

1 hour ago, RXP said:

In practice though, there are a number of people with a 3090 reporting much shorter load times and smoother flights with 64GB RAM instead of 32GB RAM, and this can only be attributed to me to having more RAM to accommodate the RAM needs of the simulator, the same RAM being otherwise amputated by some amount because of the 24GB and the DX11 driver.

 

 

So to be clear, these reports are from people with 3090's running a higher res VR headset like a G2 or Index ?  

Is it safe to assume 32Gb is enough for normal 2D use even on a high resolution screen and it is VR that is pushing the RAM needed up to 64GB  ?

 

 

[RXP 2,338]

@Glenn Fitzpatrick Most likely with G2 indeed. But this might be the case with other headsets if you're pushing for example SS scaling maybe, or it just in VR because of the way FS2020 is using DX11 for VR regardless of the headset. It is not a hard fact yet (despite the topic title) and this discussion was started only from on one of my posts in the middle of a discussion 

However given how DX11 works and some preliminary reports of people using 3090 with high VRAM usage and better performance when going from 32GB to 64GB, there must be something substantially related after all. In any case, I wouldn't recommend any one to quickly dry out the remaining RAM supplies there are LOL, but if you got the chance to borrow 32GB and compare, this might be wise trying.