That is correct. In theory it is only exceeding VAS that should lead to an OOM. If you reach the limit of VRAM you will "only" have stutters and suffer graphical errors/glitches.

 

That said, I've managed to get decent performance in P3D after som fine tuning, and I use lots of shadows and medium tessalation with good results. VRAM usage is 1,3+1,4 GB, perfect for my GTX 580.

 

For some reason P3D does not crash with an OOM now! I moved tessellation one notch from the right (before it was set to far right) -- memory requirements has also gone down from 7 gb (at time of crash) to 5.4 Gb (no crash at end of flight to Sydney, YSSY)! 

That is correct. In theory it is only exceeding VAS that should lead to an OOM. If you reach the limit of VRAM you will "only" have stutters and suffer graphical errors/glitches.

 

That said, I've managed to get decent performance in P3D after som fine tuning, and I use lots of shadows and medium tessalation with good results. VRAM usage is 1,3+1,4 GB, perfect for my GTX 580.

That is interesting....I have also the GTX660Ti but found I can medium settings with very little shadows (cockpit only)...otherwise my card load is at 90 - 99% solid. Would anyone care to share their settings?

Settings > Display > Scenery > Tessellation Factor

 

Thanks...learning something new every day.

If you haven't already, check out Beau Hollis' post today in this thread (scroll down to the sixth post on page one) - the best explanation I've seen to date on what tessellation is supposed to accomplish and how it impacts performance.  Not different from what Sebastian posted above but a little more detail about settings and tradeoffs.  Seems like we'll need to work the slider in balance with shadow and water settings in order to get the effects we want while setting some sort of reasonable limit on shader passes.  It's not unlike the water level setting in FSX, but now there are more factors (and sliders) to consider.  Have a look.  

 

EDIT: It occurs to me that clicking and scrolling might be a bit cumbersome.  Unfortunately I can't figure out how to link to an individual post on the P3D forum.  Here's what Beau has to say:

 

JD, Thanks for posting your settings. The key there is that Tessellation and shadows are disabled. While there are some big feature trade offs doing that, it will drastically reduce the workload of the GPU. The tessellation option was added in specifically as a fallback for old hardware that was better suited for v1 but needed to use the newer SDK features of v2. I had to talk Wes out of calling it "Laptop Mode"  . We did this to provide as much flexibility as possible for hardware support while still being able to build our system to take advantage of high-end hardware.

 

The tessellated terrain pages faster on the CPU-side and is required for some of the cool new stuff:
- Real-time lighting of terrain and time preview
- per-dem-point materialization for sensors and specular lighting. (eg Ice is shiny and sand isn't) This is fairly subtle unless you use the IR view and doesn't work for photo-scenery because it uses the texture generation process to create the materialization data while the textures are generated, but it does have tons of potential.
- 3D water

 

All that said, the Tessellation basically builds and renders the entire world mesh in 1 to 3 draw calls. Doing this puts a LOT of strain on the GPU, and older GPUs just don't have the pipeline bandwidth to handle it. Even new ones can struggle if you're using very high resolutions, multiple views, etc.

 

This is why terrain reflections and shadow casting are also so expensive because it has to draw the terrain multiple times.

 

Shadows in general are expensive because they basically work the way reflection views do, where the scene is rendered in another pass. Multiple passes are required for shadows though (2-12 passes depending on settings) and each pass writes out to a 2048x2048 map. We use some GPU tricks to write out to all 2-12 maps at once, but this also stresses pipeline throughput.

Very interesting post Alan. We're still scratching the surface of our understandfing...but it's damn near unbelievable that we're getting so much info directly from the devs :lol: