Intermittent low FPS in VR when textures=HIGH

[Toumal]

Hi, I'm having an issue with performance in DCS and I wanted to see if maybe others had the same experience or if I'm missing an optimization step:

 

I play with the Index on a Ryzen 3900X and a 2080Ti. When my object textures are set to high, I can fly without issue for quite some time. But at some point, very suddenly, the framerate drops from around 100fps to 2-3fps (yes, that's essentially a slideshow), and *stays that way* for a significant amount of time, usually 4-5 minutes. And then, just as suddenly as it started, it goes away again and the game is perfectly smooth. I found that I can trigger this by switching rapidly between external views of other aircraft, but it can also be triggered by landing near densely populated areas of the Syria map.

 

I tried everything, and then I discovered that switching the textures setting to medium or low makes this problem go away completely.

 

I tried using the VR optimization shaders and they work well (with the known caveats like of flood lights only rendering in one eye), but they have no effect on this phenomenon.

 

Does anyone know if there's a way to get high-res textures and NOT have this problem? Anyone experience something like this at all?

 

Please note that this has nothing to do with lots of objects on the screen. Just toggling between multiple high flying aircraft triggers it too for me, and then the low fps stays consistent regardless of what is on the screen. Is the game running out of texture memory? Is there some weird memory swapping going on maybe? Or is there some setting I can tweak (aside from texture resolution...)

 

 

EDIT: Errrgh, intended to post this in the problems forum... maybe a mod could move this please?

Edited October 18, 2020 by Toumal

[Svsmokey]

There is a good deal of discussion in the VR section of the input/output subforum here about DCS VRAM leaks .

Here for example : https://forums.eagle.ru/showthread.php?p=4509279

 

The good news is that many cannot discern a difference if ground textures are set to "low" or "high" in VR .

[twistking]

also check this thread here. it's me finding out over several pages how dcs does not do any vram management at all:

https://forums.eagle.ru/showthread.php?t=248950

 

in short, once vram is filled up, you're fu***d until you restart the game.

there are many ways to trigger that "state of low performance", skipping through multiple aircrafts or high detail ground units is probably the fastest;)

[twistking]

my theory is, that basically everybody that flies public multiplayer or large sp missions is constantly in that state of decreased performance, but that some systems with very high system memory bandwith, high system ram amount and very fast storage are better suited to plow through that while maintaining somewhat playable framerates.

 

 

i have only 4gb of vram and 8gb of system ram and can play smoothly on 1080p on very high settings, as long as the mission is small enough and i do not deliberately trigger vram buildup. if i hit that state, for me it's basically game over with sub 20fps.

it's a tragedy: as long as vram is not filled, my ancient 770gtx manages to archieve 50-60fps on very high settings 1080p, 2*msaa on caucassus. really good performance and nice visuals.

[Taz1004]

Regardless of what's causing it, you're basically running out of resources. And your system is swapping. 4-5 minutes sounds like you don't have SSD? Or your pagefile size isn't big enough.

 

If you switch to other plane's external views, you're loading his textures. In DCS that's usually about 1-4GB per plane. Nobody... maybe except ones with 3090... have enough VRAM to load everything so it has to swap. And guess what, those textures are in compressed zip files. Your system has to extract them and then load them. If you try to unzip those texture files manually in Windows, you'd see how long it takes to extract them.

 

The big zip files, I unzip and re-zip using no compression. Using utility like 7-zip. So it loads faster. At the cost of disk space.

Edited October 20, 2020 by Taz1004

[Toumal]

Regarding SSD vs. Harddrive: I run the game off of a Samsung Evo 970 NVME SSD, and the system disk is an Evo 850. The framerate has nothing to do with unzipping files, the disk is close to idle when this happens.

 

Well I went ahead and spent a few hours digging into what DCS is doing using the nvidia profiler. What happens is that it's trying its best to maximize VRAM usage which is of course desirable. I found that at high texture settings when switching airplanes there's a point when it keeps unloading and re-loading textures for each single frame. There is a literal torrent of DtoH and HtoD memcpy operations going on, which goes away just as the framerate returns to normal. This is definitely a bug in the game, as it apparently keeps textures on on the graphics card that are long since unused. It simply holds on to them for way too long even though that object is not even rendered anymore. Having more VRAM simply makes this less likely to occur, same with lowering the texture setting. It also matters which map you're running - syria is definitely one of the more resource intensive maps.

 

There's definitely something wonky with the memory management here. There's no need to hold on to the textures for an F14 that's not in view anymore.