On The Glideslope

A few weeks back I upgraded the sim software to Prepare3d 3.2, and as I posted here it generally went great but did create a few issues, one of which was a memory leak leading to out of memory errors (known as a OOM in the sim community). For those who are new to this, both Prepar3d and Flight Simulator X are 32-bit programs, meaning they are written for platforms from the first generations of powerful desktop PCs (which had 32-bit architectures). At some point this is too much inside baseball, but the important thing is that because these programs run on a legacy set of code that’s more than 10 years old, they can only access a total of about 4 gig of RAM (called VAS, for “virtual address space”). So even though my PC has 16 gig of fast memory available, the sim can only get to a portion of it.

As the sim loads scenery, other aircraft, clouds, etc., it fills that memory up, and at some point there’s not enough left for it to run and the software crashes. FSX historically isn’t great at freeing up new memory as you fly over new terrain and the old terrain is not longer visible. P3D is better. But with both, OOM errors can happen when you have lots of complex scenery, aircraft, and add-ons, so you want to preserve your available VAS memory as best you can.

Which is why the memory leak I had after the upgrade was a big deal – it was chewing through my VAS at an alarming rate, even as I was just sitting on the tarmac. At first I thought Active Sky Next was the issue, but a re-install of that seemed to run ok. Then I thought it was Multi Crew Experience, an add-on I use to talk to the computer ATC in my own voice (and that I really love). MCE runs outside of the sim software, so it shouldn’t eat VAS, but it’s in the mix so I’m looking at it. I’ve since re-installed both, and done a full reinstallation of P3D. The VAS usage is better, but still not as good as it should be, and it seems to be worse with MCE running. I’m going to spend some time this morning taking out add-on scenery, aircraft, and the rest, and then adding them back one-by-one to find out what the issue is. I’ll report here when I have it cracked.

In the meantime, there’s a good thread on VAS / OOM management here for those who want to learn more.

A day of tweaking today. The sim’s performance is pretty good – really good, actually – but I can tell when it’s stressing the CPU and GPU and the photorealistic scenery just isn’t quite as beautiful as I know it should be. With the benefit of an early start this morning I was poking around this thread on AVSIM, and as a result today’s tweaks are in two groups: processor and graphics.

In terms of the processor, I’ve been running the quad-core CPU with hyper threading on but no affinity mask and no core dedication for the add-on software (Active Sky Next, the Flight1 GTN 750 GPS, and Multi Crew Experience). After reading the AVSIM thread I set my affinity mask to 116 in the P3D.cfg file, then downloaded Process Lasso and used it to assign the add-on software to virtual cores 1, 6, and 7. This was all seamless and easy, and Lasso really is a very cool piece of software.

Then it was time for graphics. A few weeks ago I found this thread in the ORBX forums, and after making those changes then to both my P3D.cfg file and my NVIDA Control Panel I had really good performance from the sim. One key (I think) was using the NVIDIA Control Panel to set the VSync to “Adaptive 1/2 Refresh Rate,” which would make the refresh rate 30 frames per second on my 60 hz monitors. One of the things I’ve learned over the past couple of months is that you want your PC and your monitors synced up, both displaying at 30 FPS or 60 FPS or whatever it may be. Given that 30 FPS is realistic for my setup (and movie-quality besides), that’s what I’m shooting for.

So this morning I figured I’d take the advice in the AVSIM thread, set my P3D settings to VSync “on,” triple buffering “on” and FPS to unlimited, set the frame rate limit to 30 in NVIDIA Inspector, and turn off the VSync adaptive setting in NVIDIA Control Panel. The result was that my frame rates absolutely tanked. As in six or seven frames per second, tanked. Abysmal. At first I thought maybe it was the affinity mask / Lasso settings, so I backed up on those. No difference. So then I took the sim’s graphic settings back to default. No change. So then I returned the NVIDIA Control Panel and Inspector back to default, and my frame rates with high settings and some pretty hefty Active Sky Next weather were back to 45-60 frames per second.

So the problem was clearly in the NVIDIA settings. I started to re-tweak with the Inspector limit at 30 fps, and that was clearly the problem – frame rates immediately dropped back to six or seven frames per second. I don’t know why that would happen, give that I had no other limiter on frame rates, but happen it did.

In the end, I cleared all settings back to the P3D defaults in NVIDIA Inspector. In NVIDIA Control Panel I fixed my settings consistent with the ORBX thread (including setting VSync to 1/2 adaptive, which should = 30 fps for my monitors). In Prepar3d I set VSync “on,” triple buffering “on,” and frame rates “unlimited.” This flew very well – the scenery was beautiful, actually – but there were some serious stutters when making steep banking turns, as well as on approach. I set the frame rates as limited to 30 fps in the sim, and things were then smooth a silk. Gorgeous textures (amazing, really, even far out – this is P3D v 3.2 at work, perhaps?), and great frame rates set at 30 fps, dropping only to 17-14 fps or so on final approach into KSLC, with maxed-out texture and mesh settings, traffic, scenery at max, and several sets of clouds from Active Sky Next. Most important, visuals were smoooooth – gorgeous photorealistic textures, and wonderful performance all around. It really was beautiful to look at.

So, it was a day of tweaking, and some real learning went on, but in the end things look and work great. I took a few flights around KSLC after all was said and done, and they were completely fulfilling. A ton of fun, and a reminder of what a great sim flight can feel like.

Post Script: Serious props to SteveW in the AVSIM forums, who has a site here, and Patrick Jorand in the ORBX forums.