A great explanation as to DX11/DX12 variances...

[Sesquashtoo 2,846]

FYI:

VRAM is VideoRAM, aka didicated RAM on a video card

From: https://forums.flightsimlabs.com/index.php?/topic/25234-beware-of-vram-usage-in-p3d-v5/
The problem isn't with the gpus. nVidia 10 and 11 series cards are more than capable of handling all the modern graphics apis. It's with the way the new graphics API's work.
There is a video floating around where Austin Myer essentially explains the same concerns in X-Plane when running on Vulkan.

DX12 and Vulkan are both newer graphics api's that work at a much lower level on the graphics card than earlier Direct X versions (for P3D / FSX) and OpenGL (for X-plane).

They offer performance gains because they allow developers to load graphics textures directly into GPU memory rather than having to load them into slower system memory (RAM) and developers can also take advantage of other functions in the new api's that reduce cpu overheads when processing "draw calls". All these things reduce the amount of CPU processing required compared with the previous versions of the API's. The freed up CPU cycles and the faster processing of textures by the video card is what is resulting in the increased performance we see in v5.

However, because developers are now working much closer to the graphics hardware (e.g. loading textures directly into GPU memory), they now must be much more aware of how much VRAM each texture requires and they must manage the VRAM directly themselves. Previous API's did the memory management for them as the textures were in system memory and the graphics API took care of swapping textures to VRAM as and when required. The developers didn't have to worry about the amount of free VRAM and the API managed all that for them. However, the older API's had lower performance since they took up valuable CPU processing time and waited for textures to be moved back and forward between system RAM and VRAM.

It seems that with P3Dv5 it is going to be the end user's responsibility not to load too many textures to exceed their available VRAM. LM doesn't appear to have taken any measures in their code to prevent this from happening. I've had one crash to desktop on my machine so far. Not 100% it was a lack of VRAM as I didn't investigate it too much, but I run at 4K with 4x Super Sampling AA (I use a 65" screen so AA is important) and all graphics and world settings maxed out except dynamic reflections. GPU is the 2080Ti.

I'm prepared for the fact that I might have to drop a few notches once the FSLabs is released. Not because of performance reasons, as I get superbly fluid performance with FSL, but because I might see the VRAM being exceeded from time to time.

Other comments:
P3D V4.5 does not use DX12.

Apparently, per the Internet, there is a 16.25% reduction in the amount of VRAM that the sim can use.
Re: my Nvidia 1060 with 6 GB ram
16.25% reduction = .975GB
So, v5 can only use 5 GB, and per Shift_Z keys twice: “GPU Memory: 3.6/5 GB”
And, v5 is currently using 3.6 GB

Per the Internet: "I have found that the two biggest VRAM hogs are Advanced Atmospherics (TrueSky Beta) and Texture Resolution."
Re: my tests:
Advanced Atmospherics setting for San Jose, CA airport departure:
On: 4.5 GB
Off: 3.4 GB

[threexgreen 3,139]

This is an excellent post and illustrates once more how P3D is continuing to shift over to the GPU. A lot of modern games actually have a VRAM usage indicator within the graphics settings that shows the VRAM loads on the spot as you play with the settings. Some will also automatically adjust the settings to adapt to your computer's performance and one consideration here is, again, VRAM usage. There are also warnings telling you that you may encounter OOM events when you load settings which your GPU will only just be able to handle. This would be handy in P3D.

I don't know to which extent LM have optimized VRAM usage in v5, but in any case it's clear that v5 works the GPU more than previous iterations and, as you say, with DX12 VRAM management has started to require the end user's attention a lot more. Older GPUs will also struggle with v5 depending on the settings and addons used and, AFAIK, many reports of VRAM issues come from those using older GPUs which is not surprising. With P3D adopting a more contemporary state through DX12 similar to other modern games, the hardware requirements change as well and some may need to switch to newer and more beefy GPUs or be more conservative with regards to the settings they use.

Incidentally, LM are listing the 2080Ti as a recommended GPU for v5 in addition to 8+ GB VRAM which was listed for v4 already. With v5 this recommendation is becoming more important.

 

Edited April 27, 2020 by threegreen

[Christopher Low 5,352]

I would be interested to know the difference with respect to VRAM usage between 4K resolution and 1080p resolution in Prepar3D v5. I would imagine that the former requires considerably more VRAM resources than the latter, but examples of the difference would be very useful. I would be running P3Dv5 in 1080p resolution (since I do not have an insurmountable desire to become bankrupt), so that "8GB+ VRAM" is probably not accurate for my requirements.

Edited April 27, 2020 by Christopher Low

[dave2013 1,129]

Thanks for that info.

I'm betting it's the 4K resolution that's causing problems for many.

When you consider that the graphics card has to process more than twice the number of pixels for a 4K display vs a 2K(1440p) display, it's easy to see how one can run out of video memory fast.

I used a 24" 1920x1080 display for 10 years and recently upgraded to a 27" 2560x1440p display.  I wanted higher resolution mainly because of the larger screen area, not so much because the image would be so much sharper, although that is a plus. I would not even consider a 4K display as the cost and benefit would not be worth it for me.

I just wonder how much more benefit one gets from a 4K display versus the same size 2K display.  Not much IMO.  If you have a 40" display then I can see the advantage, but 4K resolution for anything 32" or smaller is overkill.

This argument is similar to the fps issue.  Some folks think they need 60fps with a flight simulator or are obsessed with fps.  I've been running 30fps locked for years and have a smooth experience.  Is it worth the time and effort to have that 50 or 60fps?  For some I suppose it is.

If you want to run 4K because you have a huge display or because you like it and think it's better, then be prepared to spend a lot of money on the most powerful graphics card you can buy.

I just shake my head at these folks complaining about running out of memory, slow texture loading, stuttering, etc. when they're using a 4K display, have high graphics settings, and a 980, 1060, or 1070 graphics card.

Dave

 

Edited April 27, 2020 by dave2013

[Farlis 2,284]

 

10 minutes ago, dave2013 said:

I just shake my head at these folks complaining about running out of memory, slow texture loading, stuttering, etc. when they're using a 4K display, have high graphics settings, and a 980, 1060, or 1070 graphics card.

I only use FullHD instead of 4K, have  a 1660 and I also run out of memory.

In an ecosystem that is heavily dependant on 3rd party add-ons you simply can't expect the user to be the one who manages the texture load. It was a total loss of judgement that Lockheed didn't equip P3D with it's own texture memory management. Going to DX12 that obviously is a must.

Edited April 27, 2020 by Farlis

[ttbq1 347]

I was wondering if P3D V5 will benefit from two 2080ti on SLI, that would be 22Gb....

[Anxarces 1]

17 minutes ago, ttbq1 said:

I was wondering if P3D V5 will benefit from two 2080ti on SLI, that would be 22Gb....

No, it will still be 11Gb. Each card needs the same data in VRAM, thus it is not doubled. They share the rendering so both cards  need the textures, etc. For example, card 1 can‘t access the memory from card 2.

Edited April 27, 2020 by Anxarces

[CFIJose 5,485]

2 hours ago, threegreen said:

Incidentally, LM are listing the 2080Ti as a recommended GPU for v5 in addition to 8+ GB VRAM which was listed for v4 already. With v5 this recommendation is becoming more important.

 

How much vRAM does the 2080TI have?

[vgbaron 3,605]

Mine has 11G - shows 9.2 in P3D

 

Vic

[Ssnake51 3]

54 minutes ago, Anxarces said:

No, it will still be 11Gb. Each card needs the same data in VRAM, thus it is not doubled. They share the rendering so both cards  need the textures, etc. For example, card 1 can‘t access the memory from card 2.

Yes, so if one was going to spend that much money they would be better off getting an RTX Titan.   That gives one 24GB vram vs the 11 GB with a 2080TI,

[regis9 4,013]

2080ti is 11gb.

I’ve been able to manage for the most part in staying within the vram limits of my 8gb gtx1070, mainly flying GA around orbx airports/regions.  However, i expect once I start flying heavy iron into detailed airports some balancing will likely be necessary.  This is at 2k resolution.
 

P3D does need to have some kind of vram outlet other than crashing though.  It’s not like a closed ecosystem game where the developer can predict what vram usage will be incurred by specific settings ahead of time.

Developers will also have to be responsible in what impact their addon has on vram.  If we get to a situation where the airport, aircraft, and whatever other addon developer are all pointing fingers at each other as the generator of excessive vram usage, we all lose. 

Edited April 27, 2020 by regis9

[CFIJose 5,485]

4 minutes ago, vgbaron said:

Mine has 11G - shows 9.2 in P3D

 

Vic

Is there an 8gig version? I have not seen one.

The 2080TI card is the recommended card by LM. This is probably why so many are confused about how much vRAM they are going to need. Once we start loading up our sims, we need to lower our settings in order to avoid an OOM error or avoid poor performance.

Isn't this, in a way, what we have been doing for over a decade?

[yvjjflores 13]

So it means that we are going back to the OOM problem of previous years with the difference that now the problem is VRAM and not RAM.

I feel that we are still imprisoned within the 32 Bits in one way or another ...!

Dawn and we'll see ...

[jmig 100]

I run a 1080P projector with a GTX 970TI with 4Gbs VRAM. According to the MSI frame and usage counters I never have gone over 2700 mb of VRAM. Yet, I still get the 'Device hug' message.

[Mroberts95 136]

Just wait til the fall when NVIDIA 3080 will have 10gb and 20gb options available and I am sure the 3080ti will probably only be a 20gb option.